Nicer default impact plot

[afiqaize]

Hi,

In many CMS papers, including the combine paper, the shown impact plots are nicer to look at. The colors are sharper. This style is not the one we get by running the default plotImpacts.py (as of v2.0.0).

It would be awesome if one of these nicer styles is included in the default script, lowering the barrier to publication quality impact plots.

Cheers,
Afiq

[ajgilbert]

I don't know exactly who is making these other macros, but we are always happy to receive pull requests with improvements :-)