HALO: Style revamp

- speech bubbles are centered
- number batches are roundand simplified, same color as in g+
- markers appear as dots above the bubble
- hiding and dimissing triggers text hints
- couple of bugfixes

WARNING: some of the drawables are good for xhdpi only for now and must
be scaled down for the other resolutions

Change-Id: Ic1ef104e3840566f9f945c38bf70eefa2b72d46e
HALO: Prevent notification acces via HALO on protected lockscreens

Change-Id: I69505a5f4f6477b16a2914074e349483a88f0692
HALO: unregister settings obeservers

Change-Id: Iae44ace1e8a3b9b28fe4b168f97e0f5cb65b8f11

cleanup

Change-Id: Id2a8d801ddb28bb75eae53bf5689681a7c72a348