Support property parameter for CodeSystem/$lookup

[paulolaup]

Is your feature request related to a problem? Please describe.
Since the CodeSystem/$lookup operation implementation already returns all properties associated with a given concept, providing the possibility of deciding what properties to return via the property parameter should be implemented.

Describe the solution you'd like
This could be achieved by just filtering the properties already retrieved using provided property parameters.

[paulolaup]

I already wrote an additional method to address this feature (mostly) and can create a pull request. However, I would like to hear your input on how to handle certain errors (properties not supported by the code system, wrong language codes etc.), as I currently don't what your general approach is regarding this.