Add possibility to open a *.mos-script instead of package.mo from packagePath

This pull request is not meant for direct merging, rather for a discussion if such a feature is interesting for you, too:
The current buildingsPy implementation can open a package from the packagePath, which I presume is meant for opening the Buildings Library. In our case, we often need to open more than one library in addition to the MSL. This implementation is still a bit rough, but it checks in case packagePath does not contain a package.mo file whether it instead contains a *.mos-script. From this script, it is thus possible to open multiple libraries.