show dock battery level if available
frameworks: add dock battery drawables for HDPI/MDPI devices

Change-Id: I8cc2cfc74548693ffbdd48447d7fa414fd451f59
SystemUI: Fix dock battery icons for phablet UI

For mdpi devices, the dock battery icon in the status bar is too large and do
not match the size of the stock battery icon:
http://img835.imageshack.us/img835/8207/screenshot2013020910320.png

This fix will have the battery dock icons resized to the right size:
http://img546.imageshack.us/img546/8302/screenshot2013020910233.png

Change-Id: Ic6ec875f4ebe29b33edf6cba6997db0ea1b70aeb
add external dock battery support

Change-Id: Ieaccc2c05488b5a500834acd89a7ea294ba55a7c