File > Import > EffectCraft Project (and .ecproj/.ecprojx given to File > Import)
merges the project into a folder named after the file, with every id shifted past
the open project's, in one undo step. Relative footage resolves next to the file;
the result lists comps, root comps, primaryComp and missing media.
offset_ids now shifts tracker Motion Targets and saturates instead of overflowing;
fix_next_id saturates too, so a damaged file can't overflow on open or import.
Menu entry translated in all four languages.
(cherry picked from commit 19c653fccc95133fb35e978a7f7f20a18c0e8c89)
(cherry picked from commit f4d36d11b0ccdfc56371a3bbd8d43d3b8281ee1b)
(cherry picked from commit c08135b2de8429693e723d065584465c459a61f9)