Adding relationships from the edit item page is broken

[artlowel]

Describe the bug
If you try to add a relationship from the edit item tab as an admin the modal it will keep loading. It looks like this was broken by #1025, where a number of observables specific to the submission where added to the modal and used to determine when to show the loading component

To Reproduce
Steps to reproduce the behavior:

1. Authenticate as an admin
2. Go to an edit item page, on the relationships tab
3. Try to add a relationship

Expected behavior
The modal should work properly both in the submission and on the edit item page.

Related work
#1025

[tdonohue]

@artlowel : Assigning this back to you for analysis & estimation. It sounds like something that should be fixed in 7.0, so I gave it a medium priority.

[artlowel]

@atarix83 Could you tell me why this setItem method was added? The item was already being set by the method that initializes the modal in the submission and on the edit item page, and was independent of anything submission related. At first sight it seems like simply removing setItem could fix this issue.

[atarix83]

@artlowel that method has been added to retrieve the item end collection when I've tried to place the lookup button, along the Add more button in the form.component. There, both item and collection are not available so I made that method. In the current implementation is not needed but we should keep in mind if we'll move the lookup button as suggested by @tdonohue here

[artlowel]

In that case we can fix it in 1 hour