Determine whether colorbar can be plotted with given metadata.
can.plot.colorbar(combined_data_range, makecmap_options)
numerical vector of length 2, the combined data range of the meshes as returned by coloredmeshes.combined.data.range
the 'makecmap_options' from the metadata field of the 'coloredmeshes', see coloredmeshes.get.md
logical, whether the metadata suffices to plot a colorbar