New options and bug fixes

@joe-goullaud

- Ability to replace *all* entities of a given type with the results of the import
- Locking around main MOC to help prevent edge cases of duplication, etc
- Bug fix for supplementary data option
- Add permanent ID acquisition to *all* background moc saves vs. just built-in methods
   - Prevents subsequent duplication issues after inserting objects in custom background operation blocks, since we are fetching existing objects by object ID in import methods

@nbonatsakis Probably should be aware of this too.