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

Per @rryan 's suggestion to remove control-object dependencies from the effects framework (https://github.com/mixxxdj/mixxx/pull/316/files#r16438349).  It didn't make sense to set samplerate in the initializers, though.

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.
44100 is correct now since the bands are initialized with 44100. 
Yo may use a const "kInitSampleRate" or similar.