Topic/reqs 420 rebase

New calculators have been created. They compute the cross-gamma for multi-curve framework with specific curves (interpolatedDoublesCurve on yield with all the curves linked to the same currency).
The PR contains also the analysis/tutorial code. It compute the profit vector using (pseudo-)historical data and different approaches (full reval, delta/gamma, delta/sum of column gamma). The results of the analysis are available in the OpenGamma Quantitative Research n.15: Interest rate cross-gamma for single and multiple curves, August 2015.

This PR replace the previous one on the same subject: https://github.com/OpenGamma/OG-Platform/pull/156

See note on constructor about asserting `_shift` > 0.