feat(android): library and title side by side on tablets, a poster that becomes the page, and predictive back

From 840 dp wide, the library and the open title share the window, so
moving between titles is one tap and the grid stays where it was; with
nothing open, the right pane says to choose one. On narrower windows, a
poster tapped in the grid grows into the title page's backdrop and
shrinks back on the way out.

The app opts into predictive back. Dragging back on a title page shrinks
the page as the gesture goes and restores it if the gesture is
abandoned.

android/app/src/main/AndroidManifest.xml

@@ -11,6 +11,7 @@
         android:name=".ProtonStreamApplication"
         android:allowBackup="false"
         android:dataExtractionRules="@xml/data_extraction_rules"
+        android:enableOnBackInvokedCallback="true"
         android:icon="@mipmap/ic_launcher"
         android:label="@string/app_name"
         android:supportsRtl="true"