feat(alerting): add median reducer to frontend

public/app/features/alerting/alert_def.ts

@@ -40,6 +40,7 @@ var reducerTypes = [
   {text: 'sum()' , value: 'sum'},
   {text: 'sum()' , value: 'sum'},
   {text: 'count()', value: 'count'},
   {text: 'count()', value: 'count'},
   {text: 'last()', value: 'last'},
   {text: 'last()', value: 'last'},
+  {text: 'median()', value: 'median'},
 ];
 ];
 
 
 var noDataModes = [
 var noDataModes = [

public/app/features/alerting/partials/alert_tab.html

@@ -42,7 +42,7 @@
 						<span class="gf-form-label query-keyword width-5" ng-if="$index===0">WHEN</span>
 						<span class="gf-form-label query-keyword width-5" ng-if="$index===0">WHEN</span>
 					</div>
 					</div>
           <div class="gf-form">
           <div class="gf-form">
-						<query-part-editor class="gf-form-label query-part width-5" part="conditionModel.reducerPart" handle-event="ctrl.handleReducerPartEvent(conditionModel, $event)">
+						<query-part-editor class="gf-form-label query-part width-6" part="conditionModel.reducerPart" handle-event="ctrl.handleReducerPartEvent(conditionModel, $event)">
 						</query-part-editor>
 						</query-part-editor>
             <span class="gf-form-label query-keyword">OF</span>
             <span class="gf-form-label query-keyword">OF</span>
 					</div>
 					</div>