ProfileList: Convert to a fragment

This is required for a future two-fragment tablet layout, and simplifies
the code a bit since the profile detail (view/edit) will be implemented
as fragments anyway.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

app/src/main/AndroidManifest.xml

@@ -12,7 +12,7 @@
         android:roundIcon="@mipmap/ic_launcher_round"
         android:supportsRtl="true"
         android:theme="@android:style/Theme.Material.Light.DarkActionBar">
-        <activity android:name=".ProfileListActivity">
+        <activity android:name=".ProfileActivity">
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />