[PLAT-3744] Shifted around the logic for curve group configurations so that one curve can have many uses (e.g. as a discounting curve and an overnight curve).

Removed the @Config annotation for CurveGroupConfiguration and CurveTypeConfiguration as they are unlikely ever to be created in isolation.
[PLAT-3745], [PLAT-3572] Indices are now constructed using information from the configurations and overnight curves are created.