Add Pathak-Wagner Regularizer to ACForce

[rcclay]

Please review the developer documentation
on the wiki of this project that contains help and requirements.

Proposed changes

This adds the Pathak-Wagner regularizer to all ACForce components, thus allowing the user to mitigate the formal infinite variance problems of this estimator. Access to this feature is done by specifying epsilon=[Real > 0] in the ACForce XML section.

What type(s) of changes does this code introduce?

Delete the items that do not apply

• New feature
• Testing changes (e.g. new unit/integration/performance tests)
• Documentation changes

Does this introduce a breaking change?

• No

What systems has this change been tested on?

Intel Xeon, RHEL7, Real and Complex builds.

Checklist

Update the following with a yes where the items apply. If you're unsure about any of them, don't hesitate to ask. This is
simply a reminder of what we are going to look for before merging your code.

• Yes. This PR is up to date with current the current state of 'develop'
• Yes. Code added or changed in the PR has been clang-formatted
• Yes. This PR adds tests to cover any new code, or to catch a bug that is being fixed
• Yes. Documentation has been added (if appropriate)

[ye-luo]

Test this please

[prckent]

Interesting