Added a new private Drag property to TfpgGDIApplication
Added a new private Drag property to TfpgGDIApplication

This allows use to easily find the TfpgDrag instance we are
working with. Same was done in X11 backend.

wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI,wkitty42/fpGUI