Add depth entry to new dive edit dialog

Add depth entry to new dive edit dialog

Christ, if you look up "Ugly dialog" on Wikipedia, I think it has a
picture of this "New dive" thing.  Or it should have.

But it kind of works.  Although with only a "max depth" entry, you can't
currently set average depths etc, so SAC-rates etc cannot be calculated
for these kinds of dives.

And the dive numbering is wrong.  We do auto-number new dives that get
added at the end, but we do it as we add them, so when you *edit* the
dive information (before it has been added) the dive number shows up as
"#0".

So there's certainly room for improvement here.

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