Animate Recents on High-End devices

This adds back the translucent background and animations
on high-end devices with more than sufficient RAM, so that
it does not feel so weird when launching recents screen.

Change-Id: I32d6b359ed374126827af03ecf4854ab2b949920

Conflicts:
	packages/SystemUI/src/com/android/systemui/recent/RecentsActivity.java