Store contributor profile data in IPFS

This stores the GitHub username and UID in IPFS, and stores the
resulting IPFS hash in the contract. Now we can remove the GitHub
profile data from the contract entirely.

app/models/contributor.js

@@ -11,6 +11,20 @@ export default Ember.Object.extend({
 
   avatarURL: function() {
     return `https\:\/\/avatars2.githubusercontent.com/u/${this.get('github_uid')}?v=3&s=128`;
-  }.property('github_uid')
+  }.property('github_uid'),
+
+  serialize() {
+    return JSON.stringify({
+      profiles: {
+        'github.com': {
+          uid: this.get('github_uid'),
+          username: this.get('github_username'),
+        }
+        // 'wiki.kosmos.org': {
+        //   username: this.get('wiki_username')
+        // }
+      }
+    });
+  }
 
 });