add dropdown component

lib/ui/checkbox.d.ts

@@ -1,11 +1,12 @@
 interface CheckboxOptions {
     type?: string;
-    label?: string;
+    label?: string | HTMLElement;
     checked?: boolean;
     isImage?: boolean;
     imageHeight?: Number;
     checkedNode?: HTMLElement;
     uncheckedNode?: HTMLElement;
+    customerAttributes?: { [key: string]: string };
     onchange?: (this: HTMLInputElement, ev: Event) => any;
 }