Migrate to fragments and improvements

- Migrate to fragments
- Fix #487
- Don't show "Open in popup mode" to channel links
- New backstack of videos
- Change the subscribers count to format using `NumberFormat`, for example some locales use `.`  others `,`, this handles it automatically (and the old method had a bug for leading zero, e.g. 4.82.125 instead of 4.082.125)
- Add string 'subscribers' for channels with more than 1 subscriber (plural)
- Popup player chooses the default format and resolution based on the new preference (format)
- Fix taskaffinity of the router activities
- Show title before loading, as it is available from the items already loaded

app/src/main/res/layout/main_bg.xml

@@ -4,7 +4,7 @@
     android:orientation="vertical" android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:id="@+id/mainBG"
-    tools:context=".detail.VideoItemDetailActivity">
+    tools:context=".fragments.detail.VideoDetailFragment">
 
     <TextView
         android:layout_width="wrap_content"