getFillText() serves to decouple the text displayed in the auto-complete list
via getText() and the text actually filled into the box via getFillText(). This
allows us to display command + args on the list but only fill the command part.
A Command class has been added to provide some structure when extracting the
command name and args. Manually tested and it works.
This is required for automatically entering tab-complete mode because
onKeyDown is NOT called in that case, so we need to make sure to have a
membership list hanging around.
David Baker