Improve default plotting

[RenHirayama]

Currently the default plotting produces weird/bad things, such as

(y-axis limits could be smaller on the latter)

I noticed this for the cross section targets, but we should check everything, so probably this has to be fixed in a case-by-case way. Also some plots would benefit from a log-scale either in x or y, or change the x variable from $\sqrt{s}$ to $p_\mathrm{lab}$ .

[RenHirayama]

I also found that the some plotting scripts consume a lot of RAM, so that I needed to ask for more (8G/cpu seems to suffice). This can probably be improved but is not urgent.