Iterate on data usage chart UI.

Switched to inflating chart views from XML, using attributes for
configuration.  Start using drawable assets for chart components
instead of manually painting.  Include hand-cut assets, and animate
between states when touched to invoke.

Clamp sweeps to valid chart ranges and prepare for sweep labels.

Bug: 4768483, 4598460
Change-Id: Ic660c35bec826eb5e3f6a1dde3cc04d8c437ef2b