Data usage app icons and details, chart labels.

Add app icons into both summary list and details pane. Also show list
of all applications merged under a UID. Draw dates on chart axis, and
avoid flashing policy sweeps when switching networks in detail mode.

Bug: 5087283, 5038812
Change-Id: I1dcd03ca85b517f8726452af8a46b4be9b3d20f1