Add basic convolution functionality
Created by: Zaharid
These are utilities to convolve a single fktable with a PDF, both for DIS and hadronic observables. This does not add higher level functionality like resolving COMPOUND files or convolutions with different hadrons.
Also add a method to retrieve the proper PDF indexing so as to contain scheme so as to contain the nonsense.
Tests would probably work better once the higher level code is implemented, which is on its way.