Dive list: don't reset column width when reloading

We set the column width in the dive list widget when we create that
widget, based on what is in the settings. And we save the current column
width back to the settings when we destroy that widget (so if Subsurface
is shut down correctly and Qt actually gets to run the destructor but not
when someone kills the program).

That means that if we recreate the dive list at any point while Subsurface
is running (and we do that a lot when you manipulate your dive list in any
way shape or form), any changes to the column widths are lost.
DiveListView::reload() explicitly calls setupUi() which reads the column
widths back from the settings - but changes made to the columns aren't
saved to the settings until we destroy the widget...

I see no reason why reload() should call setupUi(), so I'm removing that
call. Let's hope this doesn't break anything else.

Fixes #518

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
Dive list: make saving / restoring column widths actually work

It's a testament to how much I mess around with things that I hadn't
noticed that saving the column width doesn't actually work. Or actually,
saving them worked, loading them back failed as it was done too early and
the setColumnWidth() calls had no effect - and so the next time we quit
subsurface, the default width of 100 was written over all the saved
values.

This seems like an incredible hack but it has the advantage of actually
working. I look forward to someone with better insides into the inner
workings of Qt to properly fix this.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>