Toggle overmap blinking

Two new key bindings for overmap.

(1) Toggle "B"linking of overlays on overmap. Does not affect what is shown. Turns on or off the blinking.
(2) Toggle "O"verlays on the overmap. Toggles whatever would be drawn when the blink boolean is true in the draw routine.

State is saved in uistate.

I have wanted this for awhile. Getting back to playing this game. Saw other people wanted it in a few forum posts. Made a patch.