New feature/2066 edit attr modal

[luistoptal]

Pull request for issue: #2066

IMPORTANT: this is a follow up of #2082, please merge that PR before this one

Wrap the edit attr form in a modal (see comments in #2082 (review)) so that the layout and UX is a bit less cramped and (hopefully) more straightforward, and to easily solve the layout issue expressed in the conversation

How to test?

• navigate to http://gigadb.gigasciencejournal.com/adminFile/update/id/13973
• click on edit button
• interact with modal:
  • keyboard tabbing: expect focus trap on modal
  • cancel modal: return to previous state unchanged
  • click "save attribute": expect to see the updated attribute

How have functionalities been implemented?

Wrapped the edit form in a modal that gets rendered with the reponse from the actionEditAttr method of the controller, everything else remains unchanged.

A test was removed since it tested an edge case which is no longer possible. The test checked that a fringe interaction (new attribute and edit attribute being used simultaneously) did not lead to errors. I think the fact that we can remove that test is a good indication at this edge case is no longer possible, as the new layout restricts the user to handle the editted attribute before doing anything else

Any changes to automated tests?

One test was deleted, other tests stay the same as the actions to edit attributes stay the same