Add Google SSO

This pull request adds Google SSO support. There are two main changes:

1. Add the Google auth view resource
2. Make passwords optional when creating a new user. This allows an admin
to create a user without a password so that they can only login via Google.

lemur/static/app/angular/users/user/user.tpl.html

@@ -30,8 +30,7 @@
                     Password
                 </label>
                 <div class="col-sm-10">
-                    <input type="password" name="password" ng-model="user.password" placeholder="hunter2" class="form-control" required/>
-                    <p ng-show="createForm.password.$invalid && !createForm.password.$pristine" class="help-block">You must enter an password</p>
+                    <input type="password" name="password" ng-model="user.password" placeholder="hunter2" class="form-control" />
                 </div>
             </div>
             <div class="form-group">