importer add force option

forcing writing is required with only finding matches and overwriting them. This needs to include:

1. search for duplicate entry
2. replace duplicate entry
3. update all associated files

Especially the last point means, that it will probably be necessary to do this on instrument level. Or maybe not an option could be to add an 'associated connections' attribute to the SDC class, all files in the associated collections referring to the original file could be deleted upon updating the main entry.