Endpoint cleaning: remove MRP code duplication among talkers/listeners 

These commits move the duplicated MRP client code among simple, live_stream, and jackd talkers/listeners pair.

These do *not* (yet):
- make this MRP client code any prettier,
- nor it does make the talker side and listener side MRP code common.

These result in 1,500s line of code reduction and a single point of improvement or fix for MRP among the various talkers and listeners.

Run tested on simple_listene/simple_talker, build tested on other pairs of endpoints