Modify gitignore to respect dot files in /files_for_testing

Scenery::connect_nodes return () instead of EdgeIndex since it's not
needed anaywhere.

Remove example trait_test.
Doc fixes.

Optical::name returns node type as default.

Source: add name parameter.

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

Separate Dottable trait to additional file.

Doc work.
Remove no unsed function in Light.

Remove some debug meassages. Improve spectrum plot, code cleanups.

Function was completely rewritten. Fixed many clippy warnings and
reformatted code.

Fix documentation code example.

Add export function for OpticNode / Optical.