Effect order by similarity

currently the effects are ordered by the programmatic effect ID.
This feels random, since the ID is not shown. 
I prefer a order by similarity.

Now we have 
* EQs
* Fading effect 
* Misc  

this was original requested by @esbrandt at 
https://github.com/mixxxdj/mixxx/pull/373

https://bugs.launchpad.net/mixxx/+bug/1391320
Maybe add a comment to EffectBackend.h on getEffectsIds that it should be returned in the order it hsould be displayed in the UI.