All users should be signed up (and logged in) to access the "browse items" page
Context
As documented here, the AB has two flows for the "Browse Items" page depending on whether a user is signed up or not.
HHMI has request to change this functionality so that all users who can access the browse items page must be signed up users (and logged in).
With this change implemented, only the homepage can be accessed by users without an account.
Proposal
- Change permissions for accessing "Browse items" page, so everthing is behind login except the homepage, about, and professional learning
- If relevant, remove the redundant code