A simple help system

Now included a simple help system; press F1 (or h) and a small window should open to show some verrry short descriptions about commands.

Hopefully a better system will follow...

BTW, due to the method of saving the 3d data as serialized stuff, old .org files can't be opened due to class changes. Perhaps there is way around that - haven't looked as yet. DXF writer is due sometime in future but may take time. Or other method for saving stuff.

Seppo