sc: remove unnecessary includes from header
sc: remove global using declarations

Only one of these is used. Let's not leave it in the global namespace.
sc: handlers should be private

There is zero reason for these to be public.
sc: remove some old commented code from the header
sc: inherit privately from IPeerNode

I don't think we should be inheriting from IPeerNode at all, but this is
a quick fix to head off any of the nasty issues this could cause.
Merge pull request #335 from FREEDM-DGI/sc

Sc