Warn user with pop-up modal of unsaved changes

[Dananji]

Fixes #3911 ; refs #3454

This uses the modal implementation in #2977, across the following scenarios.

Changes proposed in this pull request:

• Use confirmation when editing tabbed forms in Admin Pages, Collection edit, and File-set edit

Guidance for testing, such as acceptance criteria or new user interface behaviors:

• Dashboard -> Collections
• Choose 'Edit collection' from the drop-down for one collection in the list
• Change a field in the Description tab
• Go to Discovery tab without saving the changes
• A modal pops up as follows;
  
• Click OK to go to the Discovery tab OR click on modal backdrop/hit ESC button on keyboard to close the modal

@samvera/hyrax-code-reviewers

[no-reply]

With the understanding that this is a stop-gap for the 3.0 release, and that form work is pending in the 3.0 series, let's get this in.

I'd appreciate if someone with better front-end JS expertise than I could review it.

cc: @samvera/hyrax-ui-ux-advisors

[adamjarling]

Looks good, although note I don't have a current running version of Hyrax set up to test it on. But visually looks good I'd say.

[adamjarling]

Just a thought @Dananji in the future, for shared convention if referring to a jQuery variable, how about doing var $clickedTab = ... instead of var clickedTab = ...?

[Dananji]

Yes 👍 Thanks!