feat(elasticsearch): added caret arrow for metric / group by collapse/expand options

public/app/plugins/datasource/elasticsearch/partials/bucketAgg.html

@@ -14,7 +14,11 @@
 			<span class="tight-form-item tight-form-item-xxlarge">&nbsp;</span>
 		</li>
 		<li class="tight-form-item last" ng-if="settingsLinkText">
-			<a ng-click="toggleOptions()">{{settingsLinkText}}</a>
+			<a ng-click="toggleOptions()">
+				<i class="fa fa-caret-down" ng-show="showOptions"></i>
+				<i class="fa fa-caret-right" ng-hide="showOptions"></i>
+				{{settingsLinkText}}
+			</a>
 		</li>
 	</ul>
 
@@ -22,7 +26,7 @@
 		<li class="tight-form-item last" ng-if="isFirst">
 			<a class="pointer" ng-click="addBucketAgg()"><i class="fa fa-plus"></i></a>
 		</li>
-		<li class="tight-form-item last" ng-if="!isLast">
+		<li class="tight-form-item last">
 			<a class="pointer" ng-click="removeBucketAgg()"><i class="fa fa-minus"></i></a>
 		</li>
 	</ul>