Hardcoded Nc and Nd

[Heinrich-BR]

Grid has a hardcoded number of dimensions and colours to work with. This makes it hard to create gauge field types when attempting to write simulations in other dimensionalities and gauge groups, such as in the Holographic Cosmology project

Nc and Nd are defined in QCD.h and are directly used in a number of gauge and fermion functions. Particularly for my purposes, it would be ideal to have the template in GaugeImplTypes.h include a choice of Nc and Nd (in this case the choice of Nc is already present), and the functions that compute average plaquettes and wilson loops like in WilsonGaugeAction.h use the gauge field's dimensionality from the template, as opposed to the hardcoded Nd and Nc.