SplitButton SplitButtonItem router support

[Mrtcndkn]

Add router support for SplitButtonItem.

[cagataycivici]

Available via url option;

<p-splitButton label="Save" icon="fa-check" (onClick)="save()">
        <p-splitButtonItem icon="fa-close" label="Delete" (onClick)="delete()"></p-splitButtonItem>
        <p-splitButtonItem icon="fa-refresh" label="Update" (onClick)="update()"></p-splitButtonItem>
        <p-splitButtonItem icon="fa-link" label="Angular.io" url="http://angular.io"></p-splitButtonItem>
        <p-splitButtonItem icon="fa-paint-brush" label="Theming" [url]="['Theming']"></p-splitButtonItem>
    </p-splitButton>