Only send vulnerability events if the minimum priority is gte to that specified

Fixes #770

static/js/services/notification-service.js

@@ -129,7 +129,8 @@ function($rootScope, $interval, UserService, ApiService, StringBuilderService, P
       'message': 'A {vulnerability.priority} vulnerability was detected in repository {repository}',
       'page': function(metadata) {
         return '/repository/' + metadata.repository + '?tab=tags';
-      }
+      },
+      'dismissable': true
     }
   };