Add phpunit unit tests

[hkirsman]

I think unit tests are quite fast and they could be run on git commit. The script should find find the module path for the files that are being commited so it would not trigger the whole testcase for site.

[hkirsman]

There's phpunit task in GrumpPHP https://github.com/phpro/grumphp/blob/master/doc/tasks/phpunit.md

In our case though we want to run tests inside the module where we did the update.