Framework: Create "on-the-spot" preference dialog only if needed

Right now a new instance of the "on-the-spot" preference dialog gets created
each time when the user taps on the immersive tile or each time when the
user pulls the statusbar from the right side. It should only be created if
it's really needed.

PS2: RecentsActivity clear all
PS3: Made method static and check is in SettingConfirmationHelper
	(thanks to Yamil!) + rebase ("Long press recents to switch to last
	 app"
PS4: Removed unneeded variable

Change-Id: I464edebbfec9e3452d36876ed8ef69ab915fd872
Signed-off-by: Parthipan Ramesh <parthipan.ramesh@gmail.com>