Add function to put many models in IDB

Could use a better name in Backbone.sync, but I can't think of one right
now
Fix periodization parsing of dumps
Add comparator to periodization collections
Add view for syncing data from server
Generate skolem IRI as ID for creators without IDs

This is done in toJSON so that "blank node" creators without IDs can be
saved to IndexedDB.

When we implement a toJSON method that will generate the kind of JSON-LD
that the dataset uses, we'll have to remove these.