When importing log-files we generally want to merge trips. But
when downloading and the user chose "generate new trip", that
new trip should not be merged into existing trips.
Therefore, add a "merge_all_trips" parameter to process_imported_dives().
If false only autogenerated trips [via autogroup] will be merged.
In the future we might want to let the user choose if trips
should be merged when importing log-files.
Signed-off-by: Berthold Stoeger <bstoeger@mail.tuwien.ac.at>