Fix eq apply-to-all in preferences.

* slotLoadEffectChainInSlot was deleted, so the emit did nothing.  Create
  a function to fix that behavior.
* Don't instant-apply eq and quickeffect selections -- wait for the user to hit apply.
  (Otherwise, what's the point of an apply button?)

fixes lp:1404525
this is copied from the QuickEffectRack -- it might make sense to make this a generic function that all racks have.