Add tools to both fit and analyse fits with regularised covmats

Created by: wilsonmr

After @Zaharid 's talk we want to escalate studies into unstable covmats. This will involve being able to regularize the covariance matrices using the proposed method on a more industrial scale.

Actions can be added for various analyses, just the base level function has been added to calcutils

Also since the tools will be available in the validphys structure, it is pretty trivial to add the possibility of modifying the covmats at the level of a fit (in the new fitting code)

The implementation of regularizing covmats in the fit needs to be done in a more flexible/sensible way, not hardcoded as it is now.