UploadForm and UploadFile Implementation.

The class UploadForm creates a hidden iframe which is used as a target for the form submit.

An event of type "sending" is fired after submit. On completion (iframe completed loading) a "completed" event is fired.

Upload form implements the methods getIframeTextContent, getIframeHtmlContent and getIframeXmlContent to get the content of the iframe

UploadFile fires a "changeValue" event after the selection thruogh the OS fileselector is completed

Multiple UploadFile instances are possible. The text field is readonly