Fix Quick Settings for MSim [1/2]

 - Show the data usage of active data SIM for QS
 - Immediately update QS when data subscription changes
 - Forward setDataEnabled AS-IS (see part [2/2])

Change-Id: I1c72d9955b1d068ef276386b761f7aa2d664fdc2
(cherry picked from commit 6d457b9b10d5ec605984c2a4c4e6d206be5874ee)
SystemUI: status bar brightness: store value as int

Non-automatic brightness value is stored as int, not float.

Symptom: adjust the brightness in the status bar, the brightness
         slider in the notification bar will always be set to full

Change-Id: I5f9a6e97bae2c44c3aff7c9222186a6dbda5d902
(cherry picked from commit ad84082ea32b1292c407f3908db740ee996d9333)