SlimRecents: Rework show top most task feature

recently introduced this feature needed a bit rework. Basic changes

- do not call settings provider on every preload to prevent high IO work.
  Use our observer for that
- Use internal flag logic to mark topmost task
- Move interpretation of the expanded state into the card
- Due that topmost task is always collapsed do not show expanded icon at all
- Minor cleanup

PS:
- set mFirstTask to null if it is not used

Change-Id: Ifaabc035b6b9bd2d4527d5b34a1bca9c80a74e32
SystemUI: Fix percentage charging color does not apply

How to reproduce:
Set colors to default. Try to set only charging color.

Result:
- nothing happens when you try to charge and it is out of the max and min levels

Expected behaviour
- user choosen color applies if the user charges and it is outside the max min levels

The JB style icon which was recently introduced broke the logic completely. Clean it a
bit up and apply the colors correctly depending on the choosen style.

NOTE for the future: We have since the JB style patch 2 different behaviours....text has now indication
during charge when it is outside the min max levels. All circle styles do not have this
indication. Nothing big but we are usually consistent and should think about it.

Whatever functioniallity wise it is fixed

Change-Id: I5029d09fbf1a7e4181b082ad55d9607bcf8a63cc