Practracker: usability improvements from May retrospective

We talked about a few possible improvements to practracker in our May retrospective a couple of weeks back. Here are the suggestions we came up with.

1. Practracker should have tolerances in its exceptions. For example, if an exception allows a function to be 150 lines long, then we should not cause an error until the function is (say) 155 lines long. If the function is 151-154 lines long, that should just be a warning.

These tolerances could be percentage-based, or just flat numbers.

There should be an option that makes all warnings fatal.

2. There should be an option to list unused exceptions, and exceptions that are larger than they need to be.