cleaning out needs porting and added notes file

So the needs_porting folder hasn't been touched in some time, and for many of the plugins new things have replaced them.  I've deleted six, and added a notes file with a list of the others I suspect are obsolete - and also singled out a few that really do need porting.  

Maybe delete:  `attachtest.py`, `dfbauxtite.cpp`, `digpattern.cpp`, `drawtile.cpp`, `fix-3708.cpp`, `treedump.py`, and `veinlook.cpp`
 
 To port:   `copypaste.cpp`, `hellhole.cpp`, `hotkeynotedump.py`, `itemdesignator.cpp` (partial), `position.py`