ViewComponents should render partial views
Fixes #960
[Issue #730] Attribute Routing: Flesh out attributes - Part 1

1. Added a new AttributeRouteInfo class to store all the information for
   actions that are attribute routed.

2. Added a new ReflectedAttributeRouteModel class to store all the information
   related to attribute routes in the ReflectedApplicationModel.

3. Refactored ReflectedControllerModel and ReflectedActionModel to use ReflectedAttributeRouteModel
   instead of just the attribute route template.

4. Refactored ReflectedActionDescriptorProvider to use AttributeRouteInfo and ReflectedAttributeRouteModel
   instead of just the route template.

5. Added a CombineReflectedAttributeRouteModel method in ReflectedAttributeRouteModel that handles
   combining two ReflectedAttributeRouteModel instances.

6. Removed the AttributeRouteTemplate class and moved the methods for combining attribute routes to the
   ReflectedAttributeRouteModel class.

7. Added unit tests for ReflectedActionModel and  ReflectedControllerModel that
   cover the usage of AttributeRouteInfo.

8. Added unit tests for CombineReflectedAttributeRouteModel.
[Issue #730] Attribute Routing: Flesh out attributes - Part 2

1. Unsealed the Http*Attributes so that they can be extended and customized.
2. Added the same constructors as HttpGet to the rest of the Http*Attributes.
3. Added unit tests to validate the implementations for the IActionHttpMethodProvider.
4. Added functional tests to cover extra attribute routing scenarios like a test for an
   action with an HttpDeleteAttribute on it and action with AcceptVerbsAttribute and an
   action with a custom HttpMergeAttribute implemented.