Add a project-specific phpunit.xml file

[jhedstrom]

Having a project-specific phpunit.xml file will allow developers to more quickly and readily write and run tests for their projects.

We can copy core's phpunit.xml.dist, and populate the configuration values to be project-specific.

[grayside]

Is there value in directly referencing core's config by default?

[jhedstrom]

There is, because it sets up the appropriate namespaces, classes, etc that phpunit searches for.

[jhedstrom]

That being said, I don't think we need to copy it each time, but have it be a template that lives in this project...