DGU dataset form: collection of updates from feedback

[icmurray]

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

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