SystemUI: Make battery indicator themeable

Credit to AOSPA, @David96 and @BigBrother1984

Squashed commit of:
https://github.com/AOSPA/android_frameworks_base/commit/7e3f3bb7e68b8bde3e524498e4a339934c07da94
https://github.com/AOSPA/android_frameworks_base/commit/7bc10ffa01dbbda2fd3925e7afc686f073e9007a

Signed-off-by: Chintan Shah <cgintan1998@gmail.com>