Add multibody simulation of castor wheel

CastorModel/CastorFigure_init.m

CastorModel/CastorFigure_printcastor.m

CastorModel/CastorFigure_save_figureXYZiso.m

CastorModel/derive_equilibrium.m

CastorModel/derive_kin.m

CastorModel/main.m

CastorModel/variables.m

functions/ConstraintProjection.m

functions/Lagrange.m

functions/LinePlot3.m

functions/Plot_symbolic_var_changes.m

functions/Structconv_fun2num.m

functions/Structconv_sym2fun.m

functions/TMT.m

functions/TUD_color_generate.m

functions/TriadPlot3.m

functions/rotx.m

functions/roty.m

functions/rotz.m

functions/rotz2d.m