Make sure usernames and emails are unique and message is sent to user.

endpoints/api.py

@@ -16,6 +16,11 @@ from auth.permissions import (ReadRepositoryPermission,
 logger = logging.getLogger(__name__)
 
 
+@app.errorhandler(model.DataModelException)
+def handle_dme(ex):
+  return make_response(ex.message, 400)
+
+
 @app.route('/api/')
 def welcome():
   return make_response('welcome', 200)
@@ -45,8 +50,6 @@ def create_repo_api():
 @login_required
 def list_repos_api():
   def repo_view(repo_perm):
-    
-
     return {
       'namespace': repo_perm.repository.namespace,
       'name': repo_perm.repository.name,