New functions for histogram plotting

- small fix for one of the examples (bar->hist*)
- added histogram preparation to hist_utilities
- moved latex labels to config/
- changed from TFile to rootpy.io.File
- new CMS style variables
- added electron eta plot example for cross section analysis
- added mttbar plot example (incomplete, missing QCD from data) for Z' analysis


*there is a bug regarding rootpy.plotting.root2matplotlib.hist: the hist plot will be always first (i.e. before errorbar) even if it is drawn last.