Corresponds to SpecsFor.Mvc 4.0.0-rc03

Updated SpecsFor.Mvc to MVC 5.2.2.
MvcWebApp now exposes a RemoteWebDriver rather than the lower-level IWebDriver.
Improved how validation errors are detected.
Improvements to some error messages.
Added support for changing how field validity is checked via conventions.

Renamed convention class and related methods to better-indicate what can be changed.
Bumped version number for final 4.0.0 release of SpecsFor.Mvc.