Make samplerate an explicitly-passed variable in the effects framework.

This avoids make the effects framework depend on control objects and prevents
possible sample-rate changes during effect processing.

TESTED=existing tests pass, and sanity-checked effects and sample rate changes.
read CO directly
remove unneeded function.
remove new in audio callback thread.
remove unused member
outdated comment
Merge pull request #322 from ywwg/effects-explicit-samplerate

Make samplerate an explicitly-passed variable in the effects framework.