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/fragment_channel.xml

@@ -0,0 +1,24 @@
+<?xml version="1.0" encoding="utf-8"?>
+<RelativeLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    android:layout_width="match_parent"
+    android:layout_height="match_parent"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:orientation="vertical"
+    android:title="@string/channel">
+
+    <android.support.v7.widget.RecyclerView
+        android:id="@+id/channel_streams_view"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        android:background="?android:windowBackground"
+        android:scrollbars="vertical"
+        tools:listitem="@layout/stream_item"/>
+
+    <ProgressBar
+        android:id="@+id/loading_progress_bar"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_centerInParent="true"
+        android:indeterminate="true"/>
+</RelativeLayout>