Support --extra-manifest-xml in webview and service_only bootstraps

Author: dbnicholson

doc/source/buildoptions.rst

@@ -166,6 +166,8 @@ ready.
 - ``add-source``: Add a source directory to the app's Java code.
 - ``--port``: The port on localhost that the WebView will
   access. Defaults to 5000.
+- ``--extra-manifest-xml``: Extra xml to write directly inside the
+  ``<manifest>`` element of AndroidManifest.xml.
 - ``--manifest-placeholders``: Inject build variables into the manifest
   via the ``manifestPlaceholders`` property.
 - ``--enable-google-services``: Enable the Google Services Gradle plugin.

pythonforandroid/bootstraps/service_only/build/templates/AndroidManifest.tmpl.xml

@@ -35,6 +35,8 @@
     <uses-permission android:name="com.android.vending.BILLING" />
     {% endif %}
 
+    {{ args.extra_manifest_xml }}
+
     <!-- Create a Java class extending SDLActivity and place it in a
          directory under src matching the package, e.g.
          	src/com/gamemaker/game/MyGame.java

pythonforandroid/bootstraps/webview/build/templates/AndroidManifest.tmpl.xml

@@ -36,6 +36,8 @@
     <uses-permission android:name="com.android.vending.BILLING" />
     {% endif %}
 
+    {{ args.extra_manifest_xml }}
+
     <!-- Create a Java class extending SDLActivity and place it in a
          directory under src matching the package, e.g.
          	src/com/gamemaker/game/MyGame.java