aria label added to add property button (#1464)

* 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

* capacity calculator link has been added with underline on focus

* add property is readout twice while using screenreader

* arialabel added to the add property button

* Update fulldatatables.less

* Update queryBuilder.less

* Update TableEntity.tsx

* Update ThroughputInput.less

* Update ThroughputInput.tsx

* Update ThroughputInput.test.tsx.snap

* Update ThroughputInput.test.tsx.snap

* Update AddTableEntityPanel.tsx

* Update AddTableEntityPanel.test.tsx.snap

* Update QuickstartCarousel.tsx

* Update SplashScreen.tsx

less/TableStyles/fulldatatables.less

@@ -650,4 +650,4 @@ tr:hover td.nameColumnText {
 
 .context-menu-item.icon-customize-columns {
     background-image: url(../../images/Options.svg);
-}
+}

src/Explorer/Graph/NewVertexComponent/NewVertexComponent.tsx

@@ -205,6 +205,7 @@ export const NewVertexComponent: FunctionComponent<INewVertexComponentProps> = (
                 role="button"
                 onClick={onAddNewProperty}
                 onKeyPress={(event: React.KeyboardEvent<HTMLSpanElement>) => onAddNewPropertyKeyPress(event)}
+                aria-label="Add property"
               >
                 <img className="refreshcol rightPaneAddPropertyImg" src={AddIcon} alt="Add property" /> Add Property
               </span>