gitk: Add a preferences dialog with some basic stuff
gitk: Add a preferences dialog with some basic stuff

There is a lot more that could be put in, such as a selector for
the font family etc., but this is a start.

Signed-off-by: Paul Mackerras <19a0ba370c443ba08d20b5061586430ab449ee8c@samba.org>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git