Function to add "CMS (Preliminary|Simulation) 20\d\d" and sqrt(s) blurbs to a plot

Like ``ATLAS_label(...)`` but without the cool ``SetTextFont(72)`` :(

Example of calling 

```python
from rootpy.plotting.style.cmstdr import labels
labels.CMS_label("Simulation 2012", sqrts=14)
```

![](http://www.hep.wisc.edu/~efriis/UCT2015/test/plotters/cms_blurbs.png)