Allow different package IDs (for preference intents)

Closes #515

briar-android/build.gradle

@@ -77,6 +77,10 @@ android {
 	compileSdkVersion 23
 	buildToolsVersion "23.0.3"
 
+	defaultConfig {
+		resValue "string", "app_package", "org.briarproject"
+	}
+
 	sourceSets {
 		main {
 			manifest.srcFile 'AndroidManifest.xml'

briar-android/res/xml/settings.xml

@@ -34,7 +34,7 @@
 
 			<intent
 				android:targetClass="org.briarproject.android.ChangePasswordActivity"
-				android:targetPackage="org.briarproject"/>
+				android:targetPackage="@string/app_package"/>
 		</Preference>
 
 	</PreferenceCategory>
@@ -48,7 +48,7 @@
 
 			<intent
 				android:targetClass="org.briarproject.android.panic.PanicPreferencesActivity"
-				android:targetPackage="org.briarproject"/>
+				android:targetPackage="@string/app_package"/>
 
 		</Preference>