Topic/reqs 490

Change PriceIndexCurve to be an interface and create PriceIndexCurveSimple for simple curves description (this change touched a lot of files).

Generalised PriceIndexCurveAddXXX to be able to add any type of curve. Created generator for interpolated price index curve with "anchor" and generator for curve as the multiplication of two other curves.

Extended ExportUtils to include some inflation curves.

Created demo examples and end-to-end tests for curve calibration and swap pricing in USD, including CPI data sets.