editing: allow an admin user to edit records within a browser

[GraemeWatt]

It would be useful to have the facility for an admin user to easily make minor edits to the YAML format of records from a browser (such as correcting typos or modifying/adding keywords) without going through the whole submission system and generating a new version.

Probably only the submission.yaml file should be allowed to be easily edited this way. If changes to data files are required, the normal submission system should be used (generating a new version).

It might be useful to grant "edit" permissions to trusted experts for the submission.yaml file of selected records (assigned by an admin user). Probably "edit" permissions should be granted automatically to the Coordinator/Uploader/Reviewer of a particular record.