DGU dataset form: collection of updates from feedback

[icmurray]

A collection of improvements to the dataset creation/edition form (feedback form DGU).

• [ ] validation error formatting
• [ ] geograohic coverage: add local authority
• [ ] resource format field
• [ ] resource format auto-complete
• [ ] renamed data tab -> files tab
• [ ] integrate Adris'a INSPIRE changeset, and migration scripts as part of build
• [ ] remove "discontinued" from the update frequency
• [ ] disable the disabling of save
• [ ] Remove ability to edit url on the edit-form (and remove "url not available")