Added code for handling of show / hide of columns.

The code also remembers to save in the config file.

Signed-off-by: Tomaz Canabrava <tcanabrava@kde.org>
Merge branch 'microFixes' of https://github.com/tcanabrava/subsurface
Correctly restore the column sizes in the dive list

Ordering here is important - we can't resize the columns before they are
created. On the other hand this now means that we explicitly need to
expand to the first dive shown.

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