Add Home / Launcher apps indexing

- add a BaseSearchIndexProvider to HomeSettings
- use a BroadcastReceiver for tracking add or remove of
Home / Launcher apps
- add "launcher" synonym for "home" too

- also code cleaning for DynamicIndexableContentMonitor

See bug: #16484927 Add "launcher" as a synonym for "home" in settings search

Change-Id: I819f4e5f7bd5e9a7882609206b2733ea1912fc69