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_search.xml

@@ -0,0 +1,27 @@
+<?xml version="1.0" encoding="utf-8"?>
+<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:layout_height="match_parent"
+    android:layout_width="match_parent"
+    android:name="org.schabi.newpipe.SearchInfoItemFragment"
+    tools:context=".fragments.search.SearchFragment">
+
+    <include layout="@layout/main_bg" />
+
+    <android.support.v7.widget.RecyclerView
+        android:id="@+id/list"
+        android:layout_width="match_parent"
+        android:layout_height="match_parent"
+        app:layoutManager="LinearLayoutManager"
+        tools:listitem="@layout/stream_item"
+        android:scrollbars="vertical"/>
+
+    <ProgressBar android:id="@+id/loading_progress_bar"
+        android:layout_width="wrap_content"
+        android:layout_height="wrap_content"
+        android:layout_centerInParent="true"
+        android:indeterminate="true"
+        android:visibility="gone"
+        tools:visibility="visible"/>
+</RelativeLayout>