Cherry-pick MR for !425.
Previously, the "Power and Battery" applet only checked for thepresence of PowerDevil's D-Bus services once when it starts up.This appears to (mostly?) work for applets embedded in a panel,but does not work for applets on the desktop itself.Likely there's a timing issue and applets on the desktop startsooner than PowerDevil will advertise its services.
A better way to work is for the applet to monitor the bus for whenthe relevant services appear or disappear. When observing a serviceregistered or unregistered event, the applet gets set up accordingly.
This fixes the race condition for two out of three applet parts(power profiles, inhibitions) but does not fix battery status;the data for that is coming from BatteryControlModelin plasma-workspace. A similar fix will have to be implemented there.