Add corresponding unit test.

Update & extend unit tests accordingly.

Update dependent code accordingly.

Check if all ports in light input data a real input ports of the node to
be analyzed. Otherwise data might be silently discarded. This should not
happen if the nodes are properly connected...

Update examples & tests accordingly.

Add corresponding unit test.
Closes #66

Use OpmResult defined in error module.

Further code cleanup

This cleans up the example code a little bit.
Fixed detector.export_data.
Generate diagram before performing analysis. If analysis fails,
a diagram is generated anyway.
Update various examples to use the aboe save function.

opticscnery example now exports model file (opticscenery.opm)

Edge connections still missing.

Modify gitignore to respect dot files in /files_for_testing