Add referral section to user settings

This allows those who have registered to referrer other students to Riot and have their referral counted for the campaign competition.

src/components/structures/login/Registration.js

@@ -57,7 +57,7 @@ module.exports = React.createClass({
             // URL of the riot-team-server to get team configurations and track referrals
             teamServerURL: React.PropTypes.string.isRequired,
         }),
-        teamSelected: null,
+        teamSelected: React.PropTypes.object,
 
         defaultDeviceDisplayName: React.PropTypes.string,