Update internet connectivity UI in dummy app in a more reactive approach

Based on the review !295 (merged) a nice improvement of the dummy app would be to use a more reactive programming approach to update the UI based LiveData updates. While the dummy app processes onionmasq events to update the dummy app UI, we don't combine different event streams for example for bootstrapping events and internet connectivity events. Instead in each separate event stream we ask for the current state either of the VPN bootstrapping state (in case of event handling of internet connectivity changes) or the internet connectivity state (in case of event handling of bootstrapping state changes).

Since the dummy app can be also seen as a reference for the integration of onionmasq and not only as a place for experimenting and testing, this part could be refactored up a little bit.