Filter should reset to "all" on import
When importing a roll, the filter retains the current setting.
This results in rather baffling behaviour if the user has set the filter on anything except "all" or "1 star": the lighttable view remains empty, due to all new files having default of 1 star.
With the attached patch, filter is now reset to "all" when a new roll or image is imported. This way the new file(s) show up on lighttable as expected.
Patch applies cleanly on top of both release-1.0 and master (3a4cd30778).