Blog Fragment in Navigation Drawer with Tabs

This replaces the custom layouts in the navigation drawer with a
`NavigationView` and adds a menu entry for Blogs.

A Main Blogs fragment is added that holds a `TabLayout` and a
`ViewPager`. Five tabs are already added, but they just have a single
placeholder fragment that is to be replaced by the actual fragments.

Closes #409

briar-android/res/drawable/blogs.xml

+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+        android:width="24dp"
+        android:height="24dp"
+        android:alpha="0.54"
+        android:viewportHeight="24.0"
+        android:viewportWidth="24.0">
+	<path
+		android:fillColor="#FF000000"
+		android:pathData="M13,12h7v1.5h-7zM13,9.5h7L20,11h-7zM13,14.5h7L20,16h-7zM21,4L3,4c-1.1,0 -2,0.9 -2,2v13c0,1.1 0.9,2 2,2h18c1.1,0 2,-0.9 2,-2L23,6c0,-1.1 -0.9,-2 -2,-2zM21,19h-9L12,6h9v13z"/>
+</vector>