Update contributor profiles

* Adds a new page for updating profiles
* Refactors the add-contributor component to allow for updating
  existing contributors
* Adds input labels to the contributor form and improves placeholders
* Adds event handlers for all contract contributor changes and uses them
  for updating the UI

refs #122

app/router.js

@@ -15,6 +15,7 @@ Router.map(function() {
   });
   this.route('contributors', function() {
     this.route('new');
+    this.route('edit', { path: ':id/edit' });
   });
 });