Toward regularizing color & level across battery indicators.

Each of our existing assets is slightly incorrect in some
way: inconsistent pixel jumps from one percent to the next,
inconsistent color change, etc. The only way to get it
perfectly right is to draw it programmatically.

Bug: 8504254 // inconsistent color change threshold
-- previously --
Bug: 3136046 // in Gingerbread
Bug: 3387973 // Honeycomb
Bug: 5070948 // ICS
Change-Id: I6a3e7409ecec55e10328541ecb1e9d54aebdbe96