Make the 'Add Dive' dialog at least slightly less butt-ugly

I still suspect that using spinbuttons for the time handling is the
wrong way, and I'm a bit surprised the Calendar widget doesn't have a
mode where you can see/set the time too.

But this makes things at least minimally prettier, and initializes the
time entries to the current time (which is obviously not what anybody
really wants, but looks a lot better than defaulting to "midnight" or
some other random time that *also* won't be what anybody actually
wants).

I think this might be something we can live with, although I hope
somebody with good taste comes along and say "don't use spinbuttons, do
this: xyzzy" and makes things look better yet.

Also, I have this suspicion that I should put the time/depth/duration
stuff to the right of the calendar.  Most displays are wider than they
are tall, so tall and skinny dialogs are bad especially if you have
limited vertical pixels.  I still have flashbacks to my netbook-using
days, hating applictions that did that.

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