Signal plots produce wrong figures if including channel 0 and using logarithmic y-scale

[thjsal]

For example, if including channel number 0 in to the analysis, one can get a residual plot like this:
residuals_original.pdf
when it really should look like this (note: in this example there are no counts below channel ~20):
residuals_fixed.pdf

To fix the problem one can replace lines like self._ax_resid.set_ylim([channel_edges[0], with self._ax_resid.set_ylim([_np.max([channel_edges[0],0.001]), in _residual.py. Similar fixes should probably be done in other signal plot types.

This problem was encountered by @Sidewaysgravity79 .