Ensuring source code formatting?

[paulromano]

Moving issue 20 from gitlab originally submitted by @RonRahaman:

Open question: Should we ensure that pull requests follow our source code formatting standards?

If so, we could add a format verification as a last step in the CI tests. We could specify misformatting as a yellow mark (a warning or expected error) rather than a red x.

If not, we can just periodically submit an PR where we run clang-format.