Effect enable state

This PR pipes the enable state transitions down to the effect itself.
So the effect can cleanup or init as required.

It offers also an option to bypass the raming from the effect framework at enable transitions.
An effect can set effectRampsFromDry to true and handle the required ramping itself.
This was introduced to the bitcrusher and to the bit perfect EQs

fixes https://bugs.launchpad.net/mixxx/+bug/1377705
I still think it's broken ;) it still doesn't take into account the sample rate, so the downsample parameter acts differently based on the master sample rate. Right?