feat(alerting): poc of dragable alert handles

public/app/plugins/panel/graph/graph.js

@@ -13,6 +13,7 @@ define([
   'jquery.flot.fillbelow',
   'jquery.flot.crosshair',
   './jquery.flot.events',
+  './jquery.flot.alerts',
 ],
 function (angular, $, moment, _, kbn, GraphTooltip) {
   'use strict';

public/sass/components/_panel_graph.scss

@@ -315,3 +315,8 @@
   font-size: 12px;
 }
 
+.alert-handle {
+  padding: 0.4rem;;
+  background-color: $dark-4;
+  box-shadow: $search-shadow;
+}