Why are these changes being introduced:

* Our config was allowing Terms and SearchEvents to be created and
  edited in Administrate which is not intended

Relevant ticket(s):

* https://mitlibraries.atlassian.net/browse/TCO-92

How does this address that need:

* Restricts routes which is how Administrate determins which features
  to enable
* Terms and SearchEvents cannot be created or edited in Administrate
* This still allows admins to destroy a Term in case we determine it
  contains sensitive information. SearchEvents can only be destroyed by
  destroying the associated Term and relying on Rails to cleanup the
  relationship.

Why are these changes being introduced:

* It will be convenient to have a mechansim in-app for authenticated
  users to look at our Categorizations prior to us building out custom
  reports/dashboards

Relevant ticket(s):

* https://mitlibraries.atlassian.net/browse/TCO-93

How does this address that need:

* Adds a read-only administrate dashboard for Categorizations
* Updates ability.rb to allow all authenticated users to view the
  dashboard

Document any side effects to this change:

This introduces minor changes to how Term and SearchEvents displays
througout the Dashboards. Overall I think this is an improvement, but
there may be edge cases where this change is not desired.