This change introduces ControllerContext for inside of Controllers, and
controller-specific extensibility points. ControllerContext carries with
it the model binding infrastructure needed to do all of the things that
controllers need to do.
Creates a new package 'Microsoft.AspNet.Mvc.Abstractions' which defines
APIs and contracts for core concepts and extensibility points in MVC.
Includes:
- ModelBinding
- Validation
- Model State
- Model Metadata
- Action Descriptors
- IActionResult
- Filters
- IActionConstraint