Include reference FMUs in XC

[chrbertsch]

I would suggest to include the Reference in the XC.

Before we make reporting on them mandatory (as the rules say) I would propose to start with a transition phase and ask all tool vendors to report on results for them, so that we get feedback on them and can possibly fix bugs.

After some time passed we could release a version 1.0 of the reference FMUs and make reporting on them mandatory