Labels with # not correctly interpreted by tex

plot labels like plt.ylabel('#cores') are not correctly interpreted in Tex mode (see, e.g. http://amas.web.psi.ch/docs/pyOPALTools/RingMultiBunch.html).

In https://gitlab.psi.ch/OPAL/pyOPALTools/blob/master/opal/visualization/SamplerPlotter.py#L201 we do

           isTex = mpl.rcParams['text.usetex']

            xlabel = '#samples'

            if isTex:
                xlabel = '\\' + xlabel

Do we need to do this everywhere, or should we create an "escape_tex" method, or is there a better solution?

cc: @frey_m