Add theme setting

This prepares that different themes can be added. Currently light and
dark will just use the default OK theme.

OpenKeychain/src/main/res/values-v21/themes.xml

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
 
-    <style name="KeychainTheme" parent="KeychainTheme.Base">
+    <style name="LightTheme" parent="LightBaseTheme">
         <item name="android:windowTranslucentStatus">true</item>
 
         <!-- enable window content transitions -->
@@ -12,4 +12,17 @@
         <item name="android:windowSharedElementExitTransition">@android:transition/move</item>
 
     </style>
-</resources>
+
+     <style name="DarkTheme" parent="DarkBaseTheme">
+        <item name="android:windowTranslucentStatus">true</item>
+
+        <!-- enable window content transitions -->
+        <item name="android:windowContentTransitions">true</item>
+        <item name="android:windowAllowEnterTransitionOverlap">true</item>
+        <item name="android:windowAllowReturnTransitionOverlap">true</item>
+        <item name="android:windowSharedElementEnterTransition">@android:transition/move</item>
+        <item name="android:windowSharedElementExitTransition">@android:transition/move</item>
+
+    </style>
+
+</resources>

OpenKeychain/src/main/res/values/arrays.xml

@@ -61,4 +61,12 @@
         <item>@string/key_size_custom</item>
     </string-array>
 
+    <string-array name="theme_entries" translatable="false">
+        <item>@string/theme_dark</item>
+        <item>@string/theme_light</item>
+    </string-array>
+    <string-array name="theme_values" translatable="false">
+        <item>"dark"</item>
+        <item>"ligh"</item>
+    </string-array>
 </resources>

OpenKeychain/src/main/res/values/strings.xml

@@ -50,6 +50,7 @@
     <string name="section_cloud_search">"Cloud search"</string>
     <string name="section_passphrase_cache">"Password/PIN Handling"</string>
     <string name="section_proxy_settings">"Proxy Settings"</string>
+    <string name="section_gui">"Interface"</string>
     <string name="section_certify">"Confirm"</string>
     <string name="section_actions">"Actions"</string>
     <string name="section_share_key">"Key"</string>
@@ -167,6 +168,7 @@
     <string name="label_verify_keyserver">"Verify keyserver"</string>
     <string name="label_enter_keyserver_url">"Enter keyserver URL"</string>
     <string name="label_keyserver_dialog_delete">"Delete keyserver"</string>
+    <string name="label_theme">"Theme"</string>
 
     <string name="pref_keyserver">"OpenPGP keyservers"</string>
     <string name="pref_keyserver_summary">"Search keys on selected OpenPGP keyservers (HKP protocol)"</string>
@@ -245,6 +247,8 @@
     <string name="filemanager_title_open">"Open…"</string>
     <string name="error">"Error"</string>
     <string name="error_message">"Error: %s"</string>
+    <string name="theme_dark">"Dark"</string>
+    <string name="theme_light">"Light"</string>
 
     <!-- key flags -->
     <string name="flag_certify">"Certify"</string>

OpenKeychain/src/main/res/values/themes.xml

@@ -1,9 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <resources>
 
-    <style name="KeychainTheme" parent="KeychainTheme.Base" />
-
-    <style name="KeychainTheme.Base" parent="Theme.AppCompat.Light">
+    <style name="LightBaseTheme" parent="Theme.AppCompat.Light">
         <item name="colorPrimary">@color/primary</item>
         <item name="colorPrimaryDark">@color/primary_dark</item>
         <item name="colorAccent">@color/accent</item>
@@ -16,6 +14,25 @@
         <item name="searchViewStyle">@style/MySearchViewStyle</item>
     </style>
 
+    <style name="DarkBaseTheme" parent="Theme.AppCompat">
+        <item name="colorPrimary">@color/primary</item>
+        <item name="colorPrimaryDark">@color/primary_dark</item>
+        <item name="colorAccent">@color/accent</item>
+
+        <!-- remove actionbar and title, we use toolbar! -->
+        <item name="windowNoTitle">true</item>
+        <item name="windowActionBar">false</item>
+        <!-- multi selection should overlay Toolbar! http://stackoverflow.com/a/26450875 -->
+        <item name="windowActionModeOverlay">true</item>
+        <item name="searchViewStyle">@style/MySearchViewStyle</item>
+    </style>
+
+    <style name="LightTheme" parent="LightBaseTheme">
+    </style>
+
+    <style name="DarkTheme" parent="DarkBaseTheme">
+    </style>
+
     <!-- http://android-developers.blogspot.de/2014/10/appcompat-v21-material-design-for-pre.html -->
     <style name="MySearchViewStyle" parent="Widget.AppCompat.SearchView">
         <!-- Background for the search query section (e.g. EditText) -->
@@ -40,4 +57,4 @@
         <item name="windowActionBar">false</item>
         <item name="windowNoTitle">true</item>
     </style>
-</resources>
+</resources>

OpenKeychain/src/main/res/xml/gui_preferences.xml

@@ -0,0 +1,10 @@
+<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
+    <ListPreference
+        android:persistent="false"
+        android:key="theme"
+        android:title="@string/label_theme"
+        android:entries="@array/theme_entries"
+        android:entryValues="@array/theme_values"
+        android:dialogTitle="@string/label_theme" />
+
+</PreferenceScreen>

OpenKeychain/src/main/res/xml/preference_headers.xml

@@ -1,4 +1,7 @@
 <preference-headers xmlns:android="http://schemas.android.com/apk/res/android">
+    <header
+        android:fragment="org.sufficientlysecure.keychain.ui.SettingsActivity$GuiPrefsFragment"
+        android:title="@string/section_gui" />
     <header
         android:fragment="org.sufficientlysecure.keychain.ui.SettingsActivity$CloudSearchPrefsFragment"
         android:title="@string/section_cloud_search" />