Add grep functionality

This PR adds `grep` and `listTests` commands to Intern. `grep` allows tests to be filtered by test ID. `listTests` lists all the tests that Intern will run, post filtering if `grep` is used. `grep` works from the command line and may be set in the test config file. `listTests` only works from the command line. See #123.
Also, with putting the message in the error, I also wonder if we would benefit from improved code clarity if we put the code that annotated the skipped property and dispatched the topic in the run loop, since that is where the other topics are published?