[3/3] OmniSwitch: omniswitch as default recents

OmniSwitch provides broadcast events for showing
and hiding the overlay

We need to make sure that OmniSwitch service is really
running else we will get no recents at all. Also on startup
it will take some time until the OmnISwitch service
has been started.

OmniSwitch will send a service start and stop broadcast
that will guard the usage of OmnSwitch

Change-Id: Ic2e10dce7c3a3f9e5a32bcb3499de521a26dd54a

Patchset: 2
https://gerrit.omnirom.org/#/c/5358/