Improve Discogs linking loading UX.I

[4www]

When you paste in a Discogs release URL on a track, the UI should display and indicator of what is happening.

In this case, pasting the Discogs URL is querying the Discogs database for the release.
That process takes a bit of time, such as 1 second. During this time the user has no visual/sensorial information about something being done, like nothing is happening.

Let's maybe just display a loading message in the place of the where the tags will appear when the request to Discogs' database succeeds.

Example implementation

Maybe a good place for starting is this component: https://github.com/internet4000/radio4000/blob/master/app/components/track-form/component.js#L51 and its template in the same folder.

[oskarrough]

Continuing on this, consider doing it like we do for the youtube title with automaticSetTitle() (observer) and fetchTitle() (ember concurrency task) in the same file.

Then you get loading state "for free".