Add initial calling sequence diagram

[pmai]

This adds an initial calling sequence diagram and related toolchain changes to make this work.

[chrbertsch]

Discussion at FMI Design Meeting:
the calling sequence is only partial, there might be additional calls to GetClocks necessary ... this is just a starting point
This shall not be a normative part of the standard, this has to be stated very explicitly. It is only one way of implementing it.
The numbers should be switched off in the final version, or we state that the numbers have no meaning.
Perhaps the multiple FMUs could be removed, has to be checked if we need to talk about interaction