GN-4599: prevent confirmation dialog from popping up twice.

[elpoelma]

Overview

This PR solves an issue with the confirmation dialog popping up twice upon leaving an edit route.
Specifically, it updates the isLoadingRoute to more correctly check if a RouteInfo object represents a loading route.
The isLoadingRoute function now checks for the following possible syntaxes:

• loading
• ${routename}-loading
• ${routename}_loading (new)

connected issues and PRs:

GN-4599

How to test/reproduce

• Open an agendapoint/regulatory statement
• Type some text without saving
• Leave the route
• Ensure that the confirmation dialog only pops up once.

Challenges/uncertainties

The isLoadingRoute function is quite volatile. If something changes to the internal naming of ember loading routes, the function would need to be updated.
Another possibility is to remove the routeWillChange listener after the user has pressed ok in the confirmation dialog.

Checks PR readiness

• UI: works on smaller screen sizes
• UI: feedback for any loading/error states
• Check cancel/go-back flows
• Check database state correct when deleting/updating (especially regarding relationships)
• changelog
• npm lint
• no new deprecations