[1/2] Settings: Add developer option to simulate charging state

I'm testing some things that require the phone to be in particular
charging states, so I figured I'd simulate it so I can do it when
away from a charger. Also, this will allow us to test things when
we don't actually have devices, as this simulates AC, USB, and
wireless charging.

Change-Id: Ia3163ce7a4f6fdf708718009343d30135d2fbacc