Update button rendering, move css classes to viewdata

WebCms/Views/Shared/DisplayTemplates/_ChartButton.cshtml

@@ -1,14 +1,11 @@
 @using LeafWeb.WebCms.Controllers
+@using LeafWeb.WebCms.Utility
 @model int
 @{
     var url = UmbracoContext.Current.UrlProvider.GetUrl(LeafWebPageIds.Chart);
-    var disabled = ViewData.ContainsKey("Disabled") && (bool) ViewData["Disabled"];
-    var xs = ViewData.ContainsKey("xs") && (bool) ViewData["xs"];
 }
-<a href="@url?leafInputId=@Model"
-   class="btn btn-outline-secondary @{if (xs) {<text>btn-sm</text>}} @{if (disabled) {<text>disabled</text>}}"
-   role="button"
-   @{if (disabled) {<text>title="No chart has been generated"</text>}} > 
+<a href="@url?leafInputId=@Model" @Html.Partial("DisplayTemplates/_ViewDataCssClass") role="button"
+   @if (ViewData.IsCssDisabled()) {<text>title="No chart has been generated"</text>} > 
     <span class="fa fa-line-chart" title="Charts"></span>
     <span class="d-none d-sm-inline">Charts</span>
 </a>