Refactor REPL client to reduce complexity

[alexrudd2]

This splits up a large function (complexity 21) into smaller ones within a class. The tradeoff is more LOC. What do you think?

[dhoomakethu]

This looks good to me on a first pass, I will spend some more time to see if everything is fine.

My original idea was not to bloat the core libraries with all these helpers/scripts but add them as separate projects which consumes pymodbus. It will be easier to maintain in that way.

[janiversen]

LGTM, but I will wait for @dhoomakethu

@dhoomakethu I get your point, but in that case we should move the whole REPL out as a separate repo, and I am not sure that it is worth it.

[janiversen]

If @dhoomakethu have concerns later then we will address them.

[dhoomakethu]

@janiversen yes, I had plans to move repl as an add-on package for pymodbus. I am not sure if it's worth the effort though.

[janiversen]

I think it is not worth the effort, it does in no way disturb the library.