Fix map scrolling

The osm-gps-map default is to scroll-and-recenter around the mouse position.
That is BAT SHIT CRAZY. So this implements our own scroll handling instead.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
White space and coding style adjustments for gps.c

It's just nicer this way.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>