ConsentRequirement has been renamed to BaseConsentRequirement, and

instead of defining an instance and passing in state, it's now defined

initially as a subclass that's then instantiated. Doing so makes it

easier to construct a requirement (no need to override __init__, just

set attributes and instantiate), and allows for having a standard set of

requirements that applications can further customize through subclassing.
It also gets rid of the "learn more" URL, which ended up not being needed

in current form.

Unit tests pass.