Make all the normal widgets uneditable and non-focusing

We always keep the focus on the dive list, so that the random gtk focus
handling doesn't suddenly randomly make us edit the combo boxes when the
cursor up/down keys start changing them instead of the dive list.

This means that dive location, notes and buddy/divemaster aren't
editable at all any more, but I'll fix that by making a separate dive
edit popup window.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>