Add ability to pinch outward to bring up launcher settings from the homescreen.

Patch Set 2:
Only launch settings when the interval between multitouch events is at least 500 milliseconds to prevent launching multiple instances.

Patch Set 3:
mLastMultitouch doesn't need to be static.
Define the acceptable interval between multitouch events as a constant.

Change-Id: I3f8b63c3cd8d189308c3900ef780035cfb9d82d2