RFC: Use shared base class for status indicators

Use the same class as a base for battery, wifi, wwan and other status indicators. Since status icons should look all the same, using a common base class allows to share a lot of code. Also each quicksetting in the notification drawer should look and behave the same, therefore this implements the shared base for it.

Based on !401 (closed)

This MR was opened to have a discussion on the idea, it currently updates wifiinfo and batteryinfo, but not wwaninfo (since there is currently some discussion #141 (closed))

CC: @guido.gunther