Add self-updater for github builds

mastodon/src/main/res/drawable/bg_update_download_progress.xml

@@ -0,0 +1,13 @@
+<?xml version="1.0" encoding="utf-8"?>
+<ripple xmlns:android="http://schemas.android.com/apk/res/android" android:color="?android:colorForeground">
+	<item android:id="@android:id/mask">
+		<shape android:shape="oval">
+			<solid android:color="#18000000"/>
+		</shape>
+	</item>
+	<item>
+		<shape android:shape="oval">
+			<solid android:color="?android:colorBackground"/>
+		</shape>
+	</item>
+</ripple>