added pointer to show more, reset values on new query

public/app/features/templating/editor_ctrl.ts

@@ -97,6 +97,7 @@ export class VariableEditorCtrl {
     };
 
     $scope.runQuery = function() {
+      $scope.optionsLimit = 20;
       return variableSrv.updateOptions($scope.current).catch(err => {
         if (err.data && err.data.message) {
           err.message = err.data.message;

public/app/features/templating/partials/editor.html

@@ -286,7 +286,7 @@
           <span class="gf-form-label">{{option.text}}</span>
         </div>
         <div class="gf-form" ng-if= "current.options.length > optionsLimit">
-          <span class="gf-form-label btn-secondary" ng-click="showMoreOptions()">Show more</span>
+          <a class="gf-form-label btn-secondary" ng-click="showMoreOptions()">Show more</a>
         </div>
 			</div>
 		</div>