Adding support for disabled option element used as a placeholder

Adding a CSS class called "customSelectPlaceholder" which will be applied to the customSelect &lt;span&gt; if the currently selected &lt;option&gt; element is disabled. Since from the user perspective you can't select a disabled option, this is only useful if the disabled &lt;option&gt;  was already selected during the loading of the form and is used as a kind of placeholder.