frameworks: add persistent notification when USB OTG is connected

Tapping the notification will take the user into Storage settings, and
highlight the 'Unmount' option.

Signed-off-by: Roman Birg <roman@cyngn.com>

Conflicts:
	core/res/res/values/symbols.xml

Change-Id: I257be8f61161db71c769dfa5ea78f5597aa063e8