Display options: allow configuration of wake on plug behavior (1/2)

Adds a global setting to the Display section to enable or disable wake-on-plug.
Default is disabled.  When enabled, the device will wake when the charger
is connected or disconnected.  When disabled, the device's wake state
will be left alone.

PS 2: Change wording of setting per DvT's recommendation

PS 3: Pull default value of setting from config.xml

PS 4: Reduce scope of variable

PS 5,6: Rebase

Cherry-picked from: I779a4aa4feeca87879c932be6e1fa032e4b4afc8

Change-Id: I106b7d901a788c19e08454d6231daebf3ff4872c

Conflicts:
	res/xml/display_settings.xml
	src/com/android/settings/DisplaySettings.java