Modify FindView and FindPartialView to accept ActionContext

Fixes #787
Moving to RandomNumberGenerator as CryptRandom is not supported in Mono
Remove incorrect override of `ModelMetadata.GetDisplayName()`
- this method delegates to a number of `ModelMetadata` properties
- no use cases for overriding; should not be `virtual`
- `ModelMetadata.DisplayName` override using `DisplayAttribute.GetName()` coming in next commit
Add `ModelMetadata.DisplayName` property
- value comes from `Name` property of `[Display]` attribute
- use new property in `@Html.DisplayName()` and `@Html.Label()`; remove associated TODO comments
Correct `ModelMetadata.IsRequired` to honour overrides
- subclasses would not calculate a value because `ModelMetadata` constructor
  set this property
- meant presence of a `[Required]` attribute in the model was ignored
Add more `ModelMetadata` and HTML helper tests
- add `CachedDataAnnotationsMetadataAttributesTest`
- add `CachedDataAnnotationsModelMetadataTest`
- confirm more default property values in `ModelMetadataTest`
- confirm use of `DisplayName` in `ModelMetadataTest`
- add `HtmlHelperDisplayNameExtensionsTest`
- add `HtmlHelperLabelExtensionsTest`
- add `HtmlHelperNameExtensionsTest`
RazorView should not create new ViewContext when rendering pages.

For pages that can pop back (e.g. Partial pages \ View Components), the
invoking component already creates a new ViewContext. ViewStart, Pages
and Layouts need to share the same Layout. This is required for sharing
ViewData values (such as title).

Fixes #861
Commonizing code in option provider

* Adding ValueProviderFactoryProvider and CompositeValueProviderFactory to
  maintain parity in pattern with other option types.

Fixes #818
Introducing Controller.TryUpdateModel

This changeset reintroduces some of the overloads for
Controller.TryUpdateModel.

Fixes #415
Fix StyleCop issues
[Issue #527] Revive common ActionResults - Part 1.

1. Added HttpNotFound() to Controller.
2. Updated HttpStatusCodeResult to expose the StatusCode as a property.
3. Added unit tests for HttpNotFound() and for HttpStatusCodeResult.
4. Updated the MvcSample to add an action that uses HttpNotFound().
5. Brought back HttpNotFoundResult and added unit tests for it.