not really useful yet...

Fixed tests for group. All tests pass again.

Remove example trait_test.
Doc fixes.

Optical::name returns node type as default.

This forces the usage of the "new" function to submit a name.

Separate Dottable trait to additional file.

The original graph is kept untouched.

Make some functions private.

If a port mapping was defined and group noed connected afterwards,
port maps might become invalid.

Check now if input / output nodes are half-connected.
Add unit tests accordingly.

To be used for improved port mapping.