Fix some broken translations in the dive list filter UI by adding
Q_OBJECT line to the class definitions of filter classes.
Plus simplify some strings given to translation by separating parts
like ": ".
Suggested-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
Suggested-by: Jan Mulder <jlmulder@xs4all.nl>
Signed-off-by: Stefan Fuchs <sfuchs@gmx.de>