Super softtakeover

This introduces soft takeover for the super knob effect parameter connection. 
The super knob jumps to the current value of the linked parameter on effect load. 
https://bugs.launchpad.net/mixxx/+bug/1329063
https://bugs.launchpad.net/mixxx/+bug/1335355

It also includes some soft takeover refactoring 
huh, so this class exists to manipulate existing controls?  That's a strange design.  But I guess that's the way it's set up.