Replace various module-code-snippets with generics

[KristianLyng]

A number of plumbing-parts for modules are basically copy/paste, and should be replaced with generics.

E.g.: The logic for resolving SenderMap. One small hitch is that the SenderRef (with family) uses foo.S while ParserRef uses foo.P etc, which probably means some minor refactoring, but now that we have senders, handlers, parsers, receivers and encoders, the code duplication is becoming a chore and a source of worry with regards to bugs and feature parity between modules.