Hide duplicate back/cancel button on the collection mapper page

[alexandrevryghem]

Description

Hide the Back button on the collection mapper, similar to the item mapper page. Also aligned the buttons in the same way and added icons to the item mapper buttons.

Instructions for Reviewers

List of changes in this PR:

• Aligned the cancel & save/discard buttons
• Added the same Font Awesome icons from the item mapper to the collection mapper
• Made it possible to hide the Back button on edit item pages
• Updated the hide Back button logic on comcol pages to also work for specific nested child routes. Previously this was only configurable for direct edit bitstream routes. So for example now you can hide the back button for the /collections/{uuid}/edit/authorizations/create route without automatically having to hide it for the /collections/{uuid}/edit/authorizations route
• Also updated the default edit item page to have a default margin bottom on the group of tabs similar to the comcol pages

Guidance for how to test or review this PR:

• Verify the collection mapper in the edit item view doesn't display the Back button

Checklist

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