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
If the single-eq checkbox is checked, always keep all decks' prefs in sync
Remove incorrect call
Merge pull request #437 from ywwg/eq-prefs

Fix eq apply-to-all in preferences.