manual edit of depth and time when adding / editing dives

[Dirk Hohndel]

We had quite a few requests for this feature, so I worked on this off and
on over the past month or so.

Given that I really want to cut 4.6.3 once the translators had a chance to
finish things up, I haven't pushed this to master, but instead pushed the
manualDepthTime branch to GitHub. It's "mildly tested" and ShouldWork™ -
but I guess it would make sense for more people to play with it, look at
the code (haven't done Qt/UI work in a while) and make sure that I didn't
break anything in the planner by mistake.

Please let me know what you think...

/D