HALO: new drawables for hdpi and mdpi

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

Conflicts:
	packages/SystemUI/res/drawable-hdpi/ic_launcher_clear_normal_holo.png
	packages/SystemUI/res/drawable-hdpi/ic_notify_halo_normal.png
	packages/SystemUI/res/drawable-hdpi/ic_notify_halo_pressed.png

Change-Id: I2cce50d2d3d958ba538acd6ef4e9a0a3a9da1eea