Merge pull request #964 from chrishunt/exclusive-club

Add 'invite only' site setting
FIX: Javascript errors when navigating to some topics
Fix spec doc; sends welcome email for active users
Move duplicated request to helper method
Show 'waiting approval' and don't send email

When 'must approve users' in enabled, we don't want to send an
activation email to users after they sign up. Instead, we will show them
'waiting approval' and not take an action until their account is
approved by an admin.
Test correct login behavior when pending approval
Send activation email after user approved
Notify admin of successful user approval