Fix issue #5128639: SystemUI grows by 10MB after taking a screenshot

We now do the screenshot in a separate process.

Also change the recents panel to not use hardware acceleration
on lower-end devices.  And improve how it gets shown to not
load all data up-front which results in a long delay when you have
lots of recents.

Change-Id: Ia309a90f9939e5405758621b3f7114597bd0c02a