Prevent audio players starting on startup.

Previously, (at least) Apollo was started on startup (in that it
appeared in the notification bar) because it listens to the AUDIO_BECOMING_NOISY
intent to silence itself in that case. This intent is broadcast by
AudioService when there's a user switch to silence any potential audio
players for the old user. As the system also sends around a
USER_SWITCHED intent on startup, this led to the aforementioned player
startup.
As the intent of AudioService was to act on a user backgrounding anyway,
send out AUDIO_BECOMING_NOISY as reaction to a USER_BACKGROUND intent
instead of the USER_SWITCHED intent.

Change-Id: Iba35844a1274c9dd195f104068304e6a7ffa809e
Fast Toggle : Add option to always display toggle when there are not active notification

Change-Id: If4e3247a5cf28ba7a3d9a0d1cfbd01b3db1c3ffd
Fix Notification Row Alpha Values

Change-Id: Ia22da1f81b72721bef3b0c36a5e7ccd85cff92b5
SystemUI: option to toggle dimming of the notification shade (1/2)

Allow the user to enable/disable dimming of the notification shade
pulldown. Check isHighEndGfx() to respect the default setting that
the device currently supports.

Users on low-end device may want to have this feature, while users
on high-end devices may want to disable it (possible battery life
savings and what not).

Change-Id: I730c0eea266541468d2d38ef88e136d85e1e4bfa