Add a very simple tab-widget presenting the list of known dive sites.
The table is rendered using our custom "TableView".
The (mis)uses the "LocationInformationModel". It moves the items
to be displayed (delete, name, description, number of dives) to the
front and makes the others hidden.
Moreover, it was necessary to limit the geo-tag decoration role to
the name to avoid having the icon next to each column.
Make the trash-can icon active and the name and description editable.
This is modelled after the cylinders-table code.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>
