Add EffectChainSlot parameter accessor.
Add makeEmptyChain helper to EffectRack.
Force update effect to match QuickEffectRack superknob on effect load.

Related to Bug #1395288. This at least fixes the issue where the
superknob appears to be broken after the effect is loaded. We don't have
a way to set the superknob to the effect's "default" value
currently.