Make fitting theory covmat with indices aligned with experiment covmat

Created by: RosalynLP

Addresses #1228 (closed) Closes #1228 (closed)

We want the theory covmat plots to be ordered by process because that looks better, but we want the fitting theory covmat to be automatically ordered like groups_index so it matches up with the experiment one.

To do this I made a new action which is the reordered theory covmat, which is only used for the fitting. I also removed the diagonal/block diagonal options from config because they're not in use any more.

I still need to test this.