Merge otus and refresh (cont'd)

Cleaned up and reconciled docs in [curator/README.md](https://github.com/OpenTreeOfLife/opentree/blob/master/curator/README.md) and [study-editor.js](https://github.com/OpenTreeOfLife/opentree/blob/master/curator/static/js/study-editor.js). Refactored lots of client-side logic for tracking numbered element ids (by type) and hinting at available new ids. Tested against the tree-import service to confirm nicer element ids as a result.