Try to make the equipment tab more compact

My attempts to actually set the width of the columns with the
SizeHintRole all failed - so I gave up on that and am forcing things to
work by making the texts in the header somewhat longer and then resizing
to that. Definitely not what I wanted to do - but that plus reducing the
font size gives us a much more reasonable / compact look.

I really hope that someone else can explain to me how to get the
SizeHintRole to affect the width (and not just the height - that part
worked just fine) of a the cells in a column. Then we can replace this
hack by a much better solution (that won't fail if the translated strings
look different).

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>
We had an extra column in the model for the dive list

It doesn't appear to be used anywhere, but it shows up in the UI and
confuses things.

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