Add possibility to set OMC arguments via API

[CSchoel]

There are many command line arguments for the OMC that can be set using setCommandLineOptions(string) from the OpenModelica scripting API. For some projects it is definitely desirable to be able to set these parameters (e.g. for unit checking with --unitChecking or for using the new OpenModelica frontend with -d=newInst,nfAPI.

Alternatively or additionally, we might even want to open up our API to allow users to send arbitrary commands to the OMC.