Link fix

This PR is another step towards combined  effects. 
It replaces the invert linked hint and introduces a neutral hint instead. This set a point on the knob parameter that are adopted at neural point on the super knob. 
The super knob can be driven in two modes, a neutral center mode, usually used for EQs and Filter effect, or a neutral left mode used for effects like bit-crusher. 
If you like to combine a bit-crusher with an EQ, you can set the link type of the bit-crusher knobs to new left, right or left/right mode where the neutral point (1.0) of the bit-crusher is mapped to 0.5 at the super knob.  
All this can tested with the Shade skin. 

Everything else defined in the parameter manifest (minimum, maximum, default) is a value, not a parameter value. For consistency -- should this be a value and not a parameter? Will it be easiest for effect writers to specify the value that is neutral or the parameter that is neutral? Hopefully we won't have a bunch of ```(neutral_value - min) / (max-min)``` in our various effects to calculate the neutral points.