Add network usage stats to status bar…

… [1/2] [log]

PS2:
Get the time delta between updates and use that to show
average bytes per second.

Change-Id: I69f1f94bd65b02ae19e32d9aba9e48a80d4cead0

Conflicts:
	packages/SystemUI/res/layout/status_bar.xml
	packages/SystemUI/res/values/dimens.xml
	packages/SystemUI/res/values/styles.xml