DO NOT MERGE Fixing some regressions

- Removing some legacy code with task loading
- Ensure that doze triggers are set correctly on configuration change
- Adding WCAGv2 contrast checking for deciding which foreground color to use for labels
- Bumping up the max thumbnail cache size slightly
- Fixing case where visibility state was not correct if you toggle recents too quickly

Change-Id: I5e954890d53948547842edce3c76c34d74e180a8
(cherry picked from commit e99e1009ce49caf220aa51c044ed53ac0a3b7cc6)