Add loading+error state for privacy dialog

[viddo]

Fixes #2340

The previous approach, of using the tab pane, was not very suitable for this use-case which became painfully clear when trying to accommodate the new saving and error states. So, instead I've replaced it with the same approach as done in the other dialogs, i.e. a view model to encapsulate the view logic.

Also:

• It will display a generic error message if the save fails for whatever reason
• Fixes Changing map privacy to password protected requires at least two clicks on "save settings" #2338 the bug that required two clicks to trigger events
• Bonus:
  • Permissions will only be persisted if they are actually changed
  • Fixed typo in sub title, now it states Although we believe in the power of open data, you can also protect your tables dataset. (or map), depending on viewing a dataset or map.

[viddo]

ping @xavijam @saleiva code review etc. (see description for rationale and scope)

[xavijam]

Check tests :), apart from that, go ahead 👍.

[viddo]

Backend tests, fix on the way here --> #2486

[Cartofante]

Frontend tests were OK 👍 (details)