Make add/removeSource blocking, make source lists sets

Ensure that add and removeSource complete before returning. Also make
all liveData lists sets, to ensure unique values. Finally, have one
observer for LightPackageInfoLiveData, so that even if it is added
multiple times, it will not throw an error.

Fixes: 156256341
Fixes: 156498596
Test: Flash, ensure service calls and UI do not deadlock

Change-Id: Icff73994782e08d820b88aea5736e6b0dc296f14