[PLAT-3651] Conventions for FX forward curve nodes
[PLAT-3671] Adding builder and tests for FX forward curve nodes
[PLAT-3672], [PLAT-3673] Added an instrument provider for tickers that are spreads over another ticker
[PLAT-3706] Starting to add support for FX implied curves
[PLAT-3705] FXMatrix now available to curve construction functions
[PLAT-3706] FXMatrix now supplied to curve construction functions
[PLAT-3720] Creating and testing a class that works out which currencies are in a curve configuration