Add turn off action to WiFi Tether notification

PS 2+3 : Fixed Icon + Add persistence to WiFi state [mnazim]

Adapted to LP.

Conflicts:
	core/res/res/values/slim_strings.xml
	core/res/res/values/slim_symbols.xml
	services/java/com/android/server/connectivity/Tethering.java

Change-Id: I320405ed7e90e4c06ecdb127cd4c1cad6bedbcdd
Signed-off-by: Gergely Szell (sethyx) <szell@hu.ibm.com>