Fixes for gps coordinates handling.

Reset coordinates properly when clicking undo.

When auto-completing location, only copy coordinates if they have not
been manually edited.

Set the background to red if the gps coordinates won't change, e.g.
there is a parse error, the change is too small or only whitespace
changes.

Signed-off-by: Michael Andreen <harv@ruin.nu>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>