Support circuit component model files in additional directories, support semi-classical models for a given SLH

[ntezak]

Upon compiling a QHDL file into a circuit_component file, it would be useful to support the option that this file is not installed 'globally' for all users of the same QNET distribution but just locally for each user.

[ntezak]

This is now already possible, however if one intends to embed a circuit it still needs to be installed globally. It would be best to have a sort of search path for circuit definitions.

Also, every SLH circuit model that only has oscillator degrees of freedom (including non-linear models) should have an automated way of defining a semi-classical Wigner-distribution derived SDE.