Observing Test Case Distribution

Taken from QuickCheck [manual](http://www.cse.chalmers.se/~rjmh/QuickCheck/manual_body.html#8):

> It is important to be aware of the distribution of test cases: if test data is not well distributed then conclusions drawn from the test results may be invalid.

Thus, we could consider adding [`label`](https://hackage.haskell.org/package/QuickCheck-2.9.2/docs/Test-QuickCheck-Property.html#v:label), [`classify`](https://hackage.haskell.org/package/QuickCheck-2.9.2/docs/Test-QuickCheck-Property.html#v:classify), and [`collect`](https://hackage.haskell.org/package/QuickCheck-2.9.2/docs/Test-QuickCheck-Property.html#v:collect), in the `Property` module.