Move the import of .FIT files into the 'Import log files' menu item,
where most people will be looking for it. This also naturally opens a
file selection dialog, which is more intuitive than having to select
this in the dive computer import dialog.
Also fix a bug affecting file imports if the log files contain
coordinates - the dive log needs to be set in the import data structure.
And refactor the file dialog file filters to make it more natural to add
more entries.
Requires https://github.com/subsurface/libdc/pull/72 to work.
Signed-off-by: Michael Keller <github@ike.ch>
