Prevent non-admin users from creating collections and items. And add notice to that effect

[whunter]

Prevent non-admin users from creating collections and items. And add notice to that effect.

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JIRA Ticket:
(https://webapps.es.vt.edu/jira/browse/LIBTD-2411)
(https://webapps.es.vt.edu/jira/browse/LIBTD-2413)
(:star:)

• Other Relevant Links (Meeting note, project page, related pull requests, etc.)

What does this Pull Request do? (:star:)

Prevent non-admin users from creating collections and items. And add notice to that effect

What's the changes? (:star:)

• Remove ability for non-admins to create stuff in models/ability.rb
• Redirect from GenericFiles#new and Collections#new in controllers if non-admin
• Add message to let users know of this change in layout files.
• Style message to help it get noticed by users a little better.

How should this be tested?

• Check that the new message shows up just below the header.
• Login as non-admin
• Go to dashboard page and try to upload a file to create a GenericFile record and try to create a Collection. You should be redirected back to the dashboard page in both cases
• Login as admin
• Go to dashboard page and try to upload a file to create a GenericFile record and try to create a Collection. You should be able to do this successfully.

Additional Notes:

• branch: LIBTD-2413

Interested parties

@yinlinchen
@pmather

(:star:) Required fields

[yinlinchen]

LGTM. Thanks for the quick fix! @pmather Feel free to merge if you would like

[yinlinchen]

👍

[whunter]

@yinlinchen @pmather I added redirects to all dashboard pages for non-admins. I also added them to the individual edit pages, just for the off chance that someone had a direct link to them.