Added basic channel subscription and feed pages (#620)

Added basic channel subscription and feed pages

- Room Persistence for sqlite support.
- RxJava2 for reactive async support.
- Stetho for database inspection support.
- Enabled Multidex for debug build.

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

@@ -0,0 +1,33 @@
+<?xml version="1.0" encoding="utf-8"?>
+<RelativeLayout
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:tools="http://schemas.android.com/tools"
+    android:id="@+id/channel_header_layout"
+    android:layout_width="match_parent"
+    android:layout_height="wrap_content"
+    android:layout_marginBottom="12dp">
+
+    <TextView
+        android:id="@+id/whatsNew"
+        android:layout_width="match_parent"
+        android:layout_height="50dp"
+        android:paddingLeft="12dp"
+        android:paddingRight="12dp"
+        android:drawableLeft="?attr/rss"
+        android:drawablePadding="5dp"
+        android:text="@string/fragment_whats_new"
+        android:textAppearance="?android:attr/textAppearanceLarge"
+        android:textSize="@dimen/header_footer_text_size"
+        android:gravity="left|center"
+        android:clickable="true"
+        tools:ignore="RtlHardcoded"/>
+
+    <View
+        android:layout_width="match_parent"
+        android:layout_height="1px"
+        android:layout_marginLeft="8dp"
+        android:layout_marginRight="8dp"
+        android:layout_below="@id/whatsNew"
+        android:background="?attr/colorAccent" />
+
+</RelativeLayout>