fix plenty of lint warnings, make some for loops into foreach, remove unused imports and throw exceptions

OpenPGP-Keychain/src/main/res/layout/api_app_error_message.xml

@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
-    xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent"
     android:orientation="vertical" >

OpenPGP-Keychain/src/main/res/layout/api_app_select_pub_keys_activity.xml

@@ -1,6 +1,5 @@
 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
-    xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="fill_parent"
     android:layout_height="fill_parent"
     android:orientation="vertical" >

OpenPGP-Keychain/src/main/res/layout/key_server_export.xml

@@ -1,7 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
     xmlns:bootstrapbutton="http://schemas.android.com/apk/res-auto"
-    xmlns:tools="http://schemas.android.com/tools"
     android:layout_width="match_parent"
     android:layout_height="match_parent" >