Use unit tests for --include and --exclude syntax instead of functional tests

[schlessera]

Some of tests, including but maybe not limited to --include and --exclude syntax tests, would be a better fit as unit tests. These would be more reliable and much faster.

[swissspidy]

There are now some unit tests since #83.

We might clean up the folder structure for them at some point though.

Also, there are still some Behat tests for these arguments, but I think we can keep them for now as it doesn't matter much.