Introduce TunnelToggleActivity

On Android 10, apps cannot start services when they're in the
background. This means that starting VpnService from within
QuickTileService when the app is not active ends badly. To mitigate this
situation, we introduce a proxy activity of sorts that will handle
starting VpnService for us. The activity is completely transparent and
invisible, and does only four things:

- Toggle the tunnel state
- Request the Tile bound by QuickTileService to refresh its state
- Handle any error that might have been thrown during toggle
- Call finishAffinity() and go away

Signed-off-by: Harsh Shandilya <me@msfjarvis.dev>

app/src/main/AndroidManifest.xml

@@ -26,11 +26,10 @@
         android:theme="@style/AppTheme"
         tools:ignore="UnusedAttribute">
 
+        <activity android:name=".activity.TunnelToggleActivity" android:theme="@style/NoBackgroundTheme"/>
         <activity android:name=".activity.MainActivity">
-
             <intent-filter>
                 <action android:name="android.intent.action.MAIN" />
-
                 <category android:name="android.intent.category.LAUNCHER" />
             </intent-filter>