More storage UI updates.

Storage volumes now have headers with larger fonts and progress bars
to show used versus free space.  Updated Memory to use new formatting
template, and Data Usage to use consistent display logic.

Allocate a unique color for each private volume, and yell when a
volume is running low on space.  Update private volume details to
launch into MediaStore-backed storage backends in a management mode,
and only show detailed items when hosting emulated storage.  Show
details dialog about "Other" and user storage items.

Shortcut into single private volume when it's the only device.  Add
real eject icon.

Bug: 21756698, 20275574, 21326612
Change-Id: If3ecd1d912d3e709c09d3e4da24f368e04dd3f9d