Defect2266802 (#1455)

* arialabel has been added to close button of invitational youtube video

* heading role has been addedd and tag has been changed to h1

* outline has been restored to choose columns link in entities page

* header text color changed to meet luminosity ratio requirement

* Update queryBuilder.less

* Update TableEntity.tsx

* Update QuickstartCarousel.tsx

* Update SplashScreen.tsx

* Update SplashScreen.tsx

less/TableStyles/fulldatatables.less

@@ -108,7 +108,7 @@ table.storage thead td {
     background-color: @BaseLight;
     /*[{datatable-header-background}]*/
     text-align: left;
-    color: #808080;
+    color: #333333;
     /*[{datatable-header-text}]*/
     outline: none;
 }