User roles
Can ask if a user has multiple roles
Check required_roles against user in Ability#can?
Only show subforums that the user's roles permit
WIP: fix tests
Fix user role tests
Require roles to see threads
Pull subforum required roles query into method
Use a scope instead of a method
Fix post test
Set roles when creating/updating users
Make user admin if they are HS faculty
Give faculty all roles
Setting for auto-subscribing to new threads in subscribed subforum
Subscribe to new threads in subscribed subforums by default
OAuth dance ends at originating url

Closes #122
Users can unsubscribe from subforums/threads with HTTP GET
Add unsubscribe links to emails
Fix user roles migration
Multiline block goes in do/end