Pull request for CovidSIM standalone mode

Hello Markus, we added a simple node.js standalone mode with a HTTP based REST API (or alternatively a ZeroMQ interface which is slightly but not substantially faster). Some example client code in Python is provided. Please have a look whether you think this would be useful to take over, if you want I can still change stuff as desired. In case of questions (also regarding merging with gitlab) just drop me a mail, then we can have a look.

All the best, Ferdinand