Filter effect

Hi!
I think filter effect is done. Clicks and ticks are removed, thanks to @ywwg's crossfade function.

You can listen how it sounds here: http://www.youtube.com/watch?v=nVnN0z2OXhA But in video I've used flanger's controls for changing depth end enabling effect. In this commit, I made separate controls for each decks (Flanger is still works too).

For testing you need to add knob and push button, or just download and replace "res/skins/LateNight1366x768-WXGA/skin.xml" from this commit https://github.com/xorik/mixxx/commit/4950363ca371b7c54d306c9193570e7af32acbac.

What need to do:
1) Check how it works on any controller (I think there are no problems here, just I can't test at now)
2) I don't know why, but tooltips are not worked