Bug fixes

[cippy]

There was a leftover bug from previous PR in setupRabbit.py, relevant only when using "--presel VAR:sum LOW HIGH", in particular with the ":sum" to integrate the selected axis before doing the fakes, since the axis name was propagated to other parts without removing the ":sum" key.
This had no effect on the standard CI workflow so it wasn't noticed.

Then, I am updating scripts/plotting/makeDataMCStackPlot.py with a new option to allow the user to set the x axis label (currently it is automatically read from the histogram axis, but sometimes that name is just a dummy and not informative).
Also, when using --customFigureWidth the plot function should set automatic_scale=False to make the option effective.

• about this last point, it shouldn't be needed to touch automatic_scale, but there is probably a bug in wums here [0], since "width_scale" should not appear in both the width and height items for the figure when automatic_scale = True (perhaps the correct line should read figsize=(width_scale * base_size * width, base_size * width )

[0] https://github.com/WMass/wums/blob/c7e8a11a136b4b9d0df1f6fcb21d6127a4feea72/wums/plot_tools.py#L40

[cippy]

I realised that "automatic_scale" is not already an existing key argument of plot_tools.makeStackPlotWithRatio, which is called by makeDataMCStackPlot.py.
Adding it requires touching wums to propagate it, so before doing that it would be actually better to clarify whether this line [0] is effectively a bug.
If it is, and I fix it, then there is no actual need to implement the automatic_scale key to make --customFigureWidth work properly(although it might still be useful to have "automatic_scale" configurable as a possibility).

Let me know what you prefer.

[0] https://github.com/WMass/wums/blob/c7e8a11a136b4b9d0df1f6fcb21d6127a4feea72/wums/plot_tools.py#L40

[cippy]

This PR needs WMass/wums#26 to be merged, to implement the automatic_scale flag in plot_tools.makeStackPlotWithRatio