feat(stoplight): Validation Service

This PR converts Deuce to make use of stoplight
(https://pypi.python.org/pypi/stoplight)

All the validation rules have been restructured, Especailly those around
markers and limits.
Q: How is these (QueryStringRule, RequestRule) validated to work? Where are the unit tests?

Same for their specific versions (f.e LimitRule, BlockMarkerRule)