SysUI: Allow styling of battery text/charge blend mode

Not all battery meter modes are created equally and sometimes you
need to draw the text or charge indicator using a different blend
mode than XOR.  This patch adds a new attribute to the battery
meter style which allows the blend mode to be defined per battery
style.

Change-Id: I3d2eb38828abc7e5d93337fa815a414675df43a1
TICKET: NIGHTLIES-2981
3 files changed