Currently in FileView querying the Placemark properties will present a read-only dialog. In order to allow for property modifications we need to check

- whether the matching GeoDataDocument belongs to a file that has write-access for the Marble user. 

- and we need to check whether the file has been opened via a map theme.

As a proof of concept please add a "Remove" entry to an item in the FileView if the item has write access. If the User clicks "Remove" then a dialog should be opened with a message:

- "You asked to remove [GeoDataObject]. Should this removal be temporary or saved to disc?"

- "You asked to remove [GeoDataObject]. This file is part of a map theme. Should this removal be temporary or saved to disc?

The buttons below should allow to choose between [Temporary] (which just applies the changes for the session in memory), [Save to Disk] (which saves the changes to disc) and [Don't Remove] (which cancels the operation).