Factor out the "yes/no" menu and use it for "Wipe cache" too.

It's surprising that only one of the wipe options asks for confirmation.
This change makes it easier to add confirmation to any action.

I've also removed the version information from all but the main menu,
because I find I'm not really reading the red text because there's
so much of it all the time.

(Given that fingerprints are long and menu items aren't wrapped, we
might want to go with an actual "About" menu item instead.)

Change-Id: I7d809fdd53f9af32efc78bee618f98a69883fffe