Updated windows .bat startup files

Deleted the dexen .bat file

Replaced it with two new files/ dxn3.bat optens up three command
windows, one for each dexen component (backend server, frontend server,
and node). dxn.bat opens just one command window for all three
components.
gitignore

Don't ignore the bin folder. (Even when I comment this out, I still seem
to have some trouble with this.)