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: Ib06a713e6d93649ae8c8e5be5fd62c4f44a48416

Conflicts:
	core/java/android/provider/Settings.java
	packages/SystemUI/res/values/dimens.xml

Conflicts:
	packages/SystemUI/res/values/dimens.xml
	packages/SystemUI/res/values/styles.xml
Add missing bracket
NetStats: Don't update stats when screen is off

Also moved registering of broadcast receiver and settings
observer to onAttachedToWindow() and unregistering to
onDetachedFromWindow() to avoid these being leaked.

Change-Id: Ia131a0db65c4c762b7f28493e812f9fb21358a27