MAGIC variance reduction

I added the MAGIC variance reduction technique to variancereduction.py. @makeclean, you should review the method. Tests were also added.

Theory manual addition still needed.

issue #344
Also when picking the reference flux value, my interpretation is that the reference point should be picked on the basis of the total flux, not individualy by the groupwise fluxes, I notice that in your test case that you have two regions where the flux results a normalised value of 0.5 for two regions, one in egroup 1 and another in the 2nd. Now this may be because when I and my colleague at CCFE originally implemented this, we didnt think about normalising the weight window for each energy group. Perhaps what you have done is correct, but I may have to think more about it.