improve start/stop api
As part of a fix for tpo/applications/vpn#159 (closed)
I've added a reference implementation in the dummy app to showcase how restarting onionmasq should work. In order to test you can start tor, select and deselect the browser of your choice from Settings
-> App List
and check in between if the IPs change correctly with a service as wtfismyip.com.
This MR adds a new API method Onionmasq.isRunning() which can be used to determine if ... onionmasq is already running and should be stopped before restarting it.