Adding on_delete attribute to membership models
Adding referral_url field to MembershipDefault model
Removing unused code in event_tags.py
Renamed membership referer_url field
Made a new membership view to handle referer URLs

- This view will eventually set a session item; currently commented out within this commit.
Made new event reg config method has_member_price
Setting and getting membership referee url from session
Changing variable name to something more descriptive in memberships/views.py
Store membership referer URL as relative-URL if possible
Send approval email when approving memberships from detail page
Adding context variable 'referer_url' to membership notices
Adding "continue message" on membership confirmation page

Message only shows if membership referer url is populated
Adding "referer_url" to membership notice context
Showing "become a member" link on events page

- This link is only visible if the membership has a member price.
Only showing "become member" link if detected as non-member
Log in users on membership confirmation page

- We record this in event logs
- You are only logged in if you are anonymous