Iterate over copy of packageBroadcastReceiver receivers

Ensure that we do not get a concurrentModificationException when
receiving a package added or removed broadcast, as this might cause a
concurrentModificationException as we iterate over the listeners. Also
posts all calls to add or remove listeners to the main thread.

Fixes: 154422428
Test: All screens continue to function as expected
Change-Id: I19e22f0d844e4d7f5433a3f11b1c03ad0fe0081c