Escaping \% in contourp()

[AstroRobin]

in splotch.contourp(), the following lines need a check for the 'usetex' rcParam from matplotlib as to whether the percentage symbol should be escaped or not.

if plabel is None:
	plabel=[f'{round(p,1)}\%' for p in percent]

[MBravoS]

Fixed now on the current 0.5.0.0 on the devel branch.