HALO cleanup + HALO: new drawables for hdpi and mdpi

HALO cleanup: hdpi and mdpi drawables were inconsistent, if you plan to use HALO on
lower res devices you must reproduce them.

HALO new drawables:
- scaled down the xhdpi drawables properly for hdpi and mdpi
- removed some old and unused halo pngs

Change-Id: Iff405db17cf650fa485c7a2cc0b59755415003ab