Edit collection item template

[Atmire-Kristof]

References

This PR closes #662

Description

This PR adds the ability to edit the template item of collections.
This PR is something we created a while back, but was never completely finished due to the reduced priority of the item template feature. However, this PR fixes issue #662, so we'd like to contribute this now.

Instructions for Reviewers

Changes made:

• Added ItemTemplateDataService
• Added EditItemTemplatePageComponent at route /collection/${collection-uuid}/itemtemplate. This page displays the metadata of the collection's template item and the ability to edit them (similar to edit metadata of a regular item, it uses the same child component)
• Added template item section on top of the edit metadata page of a collection. When no template item is present yet, an "Add" button is displayed. Clicking this button will create a template item and redirect the user to the edit page. When a template item is present, an "Edit" and "Delete" button will be displayed.

How to test:

• Go to a collection's edit page
• Create a new template item and edit some of its metadata
• Go back to the collection's edit page, it should now show an "Edit" and "Delete" button
• Clicking "Edit" should bring you back to the edit metadata page of the template item
• Clicking "Delete" should delete the template item
• Starting a new submission in a collection that contains a template item should fill in the metadata from the template item automatically into the new submission. But that doesn't work at the moment: Collection template item metadata not used in the submission UI #748. That's unrelated to this PR

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[lgtm-com]

This pull request introduces 3 alerts and fixes 7 when merging b77fd69 into 2fe9965 - view on LGTM.com

new alerts:

• 3 for Unused variable, import, function or class

fixed alerts:

• 7 for Unused variable, import, function or class

[lgtm-com]

This pull request fixes 10 alerts when merging 92e47de into 2fe9965 - view on LGTM.com

fixed alerts:

• 10 for Unused variable, import, function or class

[tdonohue]

👍 Looks good to me. I've tested and this both fixes #662 and adds in Item Template functionality. The Item Template functionality works as described, though there are two known bugs (already created): #750 (which is referenced by TODOs in the code) and #748 (which is out of scope for this PR)