HPCC-2851 Multi file upload/download

TODO:  Swap the content of DropZoneWidget and DropZonesWidget...

Signed-off-by: Gordon Smith <gordon.smith@lexisnexis.com>
file upload feature with disabled states and file list. File list should be incorporated with a widget.
testing multi-file upload with Kevin's changes.
dynamic form action added dependant on tab properties