Make synchronous channels work for process families

[javierdiaz72]

In #114, support for synchronous channels was added. However, this support currently works only for plain processes. We shall make synchronous channels also work for process families.

[jeltsch]

I’m not sure whether we should do that. My intention was to have only a typed, non-family version for such higher-level constructs. However, this leads us to working with closed processes only, and it might not be a good idea to exclude open processes, because it may prevent us from using results we’ve proved in other proofs. I guess that this whole concept of process families vs. just processes has to be thought through more, and we don’t have the time anymore to do so.