Stable branch from Artur's

This takes Artur's latest branch, i.e. feature/MixedPrecision, and rolls back a bit, to the point right before mixed precision started to be introduced. This rolled-back code has been tested locally (laptop) and on aicomp04, and it converges well. These first tests are with the 8^4 config file from the repo. More tests with larger lattices are coming soon, at least on aicomp04, before the merge of this MR