Add file naming dialog for save as

When right clicking a dive on the divelist a dialog for selecting a dive
was opened. However, Save As requires a getSaveFileName dialog so that
user can give a new file name as well as selecting an old file to
overwrite.

Signed-off-by: Miika Turkia <miika.turkia@gmail.com>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>