epic/referrals

• Create table to store referrals data
• Add referral to table when user registers within 24 hours of clicking a referral link
• Update referral when the prospect joins rewards program
• Update referral when referrer sends prospect 'ping' notification reminder to join rewards
• Trigger notifications to be sent to referrer when the prospect changes state (pending > complete)
• Trigger notification to be sent to prospect when referrer clicks 'ping' button
• Increase contribution multiplier from 10 to 50 for referrals
• Award one token to everyone when they join rewards program (whether or not referral)
• Add referral question/answer to FAQs (and fixed some typos)

Closes: #614 (closed), #585 (closed), #584 (closed), #583 (closed)

🚧 not ready until @markeharding gives the prospect +50 and migrates old referrals data 🚧