Allow GateKeeper to be optional

[cameron-dunn-sublime]

Describe the change
Allows gatekeeper to be omitted -- this allows it not to be run at all vs. partially unused on a request basis.

Describe testing procedures
Describe the tests that you ran to verify your changes (including test configurations) and instructions so we can reproduce the tests. To assist in testing, the project maintainers may ask for file samples.

Sample output
If this change modifies Strelka's output, then please include a sample of the output here.

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of and tested my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings