First version of automatic contact discovery.

TODO:
- Configuration (much of it)
- Enabled by default?
- Which keys to import? Current state: All non-revoked and non-expired with matching userid
- Search for keys if already known? Current state: yes, may cause traffic (configuration: only when wifi?)
- Update interval: Currently Android handles it, might be good (causes automatic refresh on new contact and stuff like that) or bad (too many of refreshes)

OpenKeychain/src/main/AndroidManifest.xml

@@ -53,6 +53,10 @@
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
     <uses-permission android:name="android.permission.NFC" />
     <uses-permission android:name="android.permission.GET_ACCOUNTS" />
+    <uses-permission android:name="android.permission.AUTHENTICATE_ACCOUNTS"/>
+    <uses-permission android:name="android.permission.MANAGE_ACCOUNTS"/>
+    <uses-permission android:name="android.permission.READ_SYNC_SETTINGS"/>
+    <uses-permission android:name="android.permission.WRITE_SYNC_SETTINGS"/>
     <uses-permission android:name="android.permission.READ_CONTACTS" />
 
     <!-- android:allowBackup="false": Don't allow backup over adb backup or other apps! -->
@@ -435,6 +439,28 @@
             </intent-filter>
         </service>
 
+        <service android:name=".service.DummyAccountService">
+            <intent-filter>
+                <action android:name="android.accounts.AccountAuthenticator"/>
+            </intent-filter>
+            <meta-data
+                    android:name="android.accounts.AccountAuthenticator"
+                    android:resource="@xml/account_desc"/>
+        </service>
+
+        <service android:name=".service.ContactSyncAdapterService">
+            <intent-filter>
+                <action android:name="android.content.SyncAdapter"/>
+            </intent-filter>
+
+            <meta-data
+                    android:name="android.content.SyncAdapter"
+                    android:resource="@xml/sync_adapter_desc"/>
+            <meta-data
+                    android:name="android.provider.CONTACTS_STRUCTURE"
+                    android:resource="@xml/custom_pgp_contacts_structure"/>
+        </service>
+
     </application>
 
 </manifest>