git-gui: Starting translation for Norwegian

This file have been used locally for some time, and is near
completion. Will put an effort into completing it later on,
or just leave it as an excercise for other Norwegians.
Signed-off-by: NFredrik Skolmli <fredrik@frsk.net>
Signed-off-by: NShawn O. Pearce <spearce@spearce.org>