Bugs on Collection Item Template fix

[Raf-atmire]

References

• Fixes Several bugs on collection's item template  #1034

Description

This PR fixes all the bugs listed in the above mentioned issue with regards to the Collection's item template

Instructions for Reviewers

List of changes in this PR:

• Ensured that the Item template is getting used in the edit template item screen instead of the collection's metadata
• Ensured that adding/deleting metadata works properly without errors
• Ensured that the delete call only returns one notification

How to test this PR

• Build this Angular branch
• Go to a collection and create an Item template
• Add and delete metadatavalues, ensure that it works
• Delete the item template afterwards, ensure that only one notification is shown

Checklist

• My PR is small in size (e.g. less than 1,000 lines of code, not including comments & specs/tests), or I have provided reasons as to why that's not possible.
• My PR passes TSLint validation using yarn run lint
• My PR doesn't introduce circular dependencies
• My PR includes TypeDoc comments for all new (or modified) public methods and classes. It also includes TypeDoc for large or complex private methods.
• My PR passes all specs/tests and includes new/updated specs or tests based on the Code Testing Guide.
• If my PR includes new, third-party dependencies (in package.json), I've made sure their licenses align with the DSpace BSD License based on the Licensing of Contributions documentation.

[atarix83]

thanks @Raf-atmire for this PR

I had a look to the code and it seems good. I've also checked that all problems are resolved with this PR