restructure MathObject classes; add VariableSlider
restructure MathObject classes; add VariableSlider

stardust66/math3d,stardust66/math3d,stardust66/math3d,ChristopherChudzicki/math3d,ChristopherChudzicki/math3d,stardust66/math3d,ChristopherChudzicki/math3d,ChristopherChudzicki/math3d