It's customary for menu bars to not have icons.
Some items were lacking icons when there's perfectly good stock icons
available. I was a bit torn between the "new" and "add" icons for the
"add dive" item, since what it really does is create a new dive, but
the "add" icon is an uninteresting sheet of paper in the default icon
theme so I decided to use the "add" icon.
Signed-off-by: Mikko Rasa <tdb@tdb.fi>