Slim Recents: add icon cache, fix FC, improve overall performances

- add back kufi LRU cache implementation to improve performances
- adapt it to the new iconpack code
- allow to clear the whole cache when changing the iconpack
23 Mar 2017:
- code cleanup
- set max cache size to 1/6 max maxMemory
- we use drawables for app icons, let's handle drawables also into the cache
without bitmap to drawable conversions

24 Mar 2017:
Fix SystemUI fc:
03-23 23:34:49.053 24500  9597 E AndroidRuntime: FATAL EXCEPTION: AsyncTask #183
03-23 23:34:49.053 24500  9597 E AndroidRuntime: Caused by: java.lang.IllegalStateException: Cannot call this method while RecyclerView is computing a layout or scrolling
03-23 23:34:49.053 24500  9597 E AndroidRuntime:        at android.support.v7.widget.RecyclerView$Adapter.notifyItemChanged(RecyclerView.java:6361)
03-23 23:34:49.053 24500  9597 E AndroidRuntime:        at com.android.systemui.slimrecent.RecentPanelView$CardLoader.addCard(RecentPanelView.java:1166)

25 Mar 2017:
Move some settings checks from doInBackground to SettingsObserver
no need to check this Settings values for each card in the
doInBackground async task, we can load them with our existing
RecentController SettingsObserver.
Less work for the background async task = better performances.

SpiritCroc edit:
- Code style improvements
- Add a second settings observer that doesn't close recents as a more reliable way
  to keep panel open when changing favorites
- Remove double vibration on favorite app toggle because of two longclick listeners
  when we're already here (same like here: http://gerrit.aicp-rom.com/#/c/34794/ )

Change-Id: I859bb5cad74acbcdda44ebd272dba5c1824a3028