Adds expire/renew actions to Permission admin pages.

Also removes UserBit admin customizations since they aren't even in the admin
panel anymore.  Resolves #1031.
Fix PermissionAdmin search fields

The 'program' search field was failing with a TypeError "Related Field
has invalid lookup: icontains"; replace it with 'program__url'
instead, which works.
Merge pull request #1228 from learning-unlimited/permission-admin-actions

Adds expire/renew actions to Permission admin pages.