Sitv

Hello Ted,

The merging of this branch to master concludes the test of running limits with the sitv cut in the analysis.

The biggest changes were made to configuration/signal.py where I had to accommodate new TDirectory names given to us by Chris/Darren.  There is now an aT attribute the the scan class.  There is also a "extraVars" attribute, this is where I put "SITV".  

I've made sure to test for backwards compatibility. That said, if Chris drops the word "SITV" from the TDirectory names, then we could get rid of extraVars to keep the code simple, if you like. 

The fZinv taken from MC is now HT dependent. (two character change :)

Best,
Yossof