Leg length slider (Illustrious)

Release candidate.

I've only recently managed to get LECO to create sliders without it cursing at me in Python about a year late to the party. Allow me to apologize in advance if the quality is not up to my usual standards.

The effect is rather slight so you can crank the strength to -+10 easily. Beyond absolute values of 15 image quality begins to degrade.

The extreme negative end (~below -20) also starts invoking umprompted chibi stuff so watch out for that.