Clean up `AssociatedMetadataProviderTest`
- remove unused nested class `ModelWithReadOnlyProperty`
- remove unecessary nested classes `RangeAttribute` and `RequiredAttribute`
- use `Assert.NotEmpty()` and `Assert.Single()` where appropriate
Reacting to System.IO package version change
Add `ModelMetadata.HasNonDefaultEditFormat` property
- add `DataType` property to `CachedDataAnnotationsMetadataAttributes` in support of `ComputeHasNonDefaultEditFormat()`
- provide doc comments and flesh out the implementation of `DisplayFormatString` and `EditFormatString`

nits:
- add comment about _not_ overriding `ComputeIsComplexType()` in `CachedDataAnnotationsModelMetadata`
- restore alphabetic order in `CachedDataAnnotationsMetadataAttributes`
- seal `SimpleDisplayText` in `CachedModelMetadata<TPrototypeCache>`, matching MVC 5.2
Move two recently-added `[HiddenInput]` tests into `CachedDataAnnotationsModelMetadataProviderTest`
Test `DisplayFormatString`, `EditFormatString`, and `HasNonDefaultEditFormat`
- `DisplayFormatString` and `EditFormatString` now based on attributes
- `HasNonDefaultEditFormat` is new
- confirm `DataType` and `ScaffoldColumn` in `CachedDataAnnotationsMetadataAttributes`
Address TODO item with new `HasNonDefaultEditFormat`
- avoid overriding a datetime format if format was already customized
- primarily affects the default Date and Time editor templates because they
  are often used due to `[DataType]` attributes with "default" edit formats
Back `HtmlHelper.Html5DateRenderingMode` with new `ViewContext` property
- provides expected scoped semantics
- helps a bit with #448 but does not provide an app-wide default
Test data/time templates
- focus on affect of `ModelMetadata.HasNonDefaultEditFormat` and
  `IHtmlHelper.Html5DateRenderingMode`
- work through `TemplateRenderer` because individual templates only do
  formatting in a few cases
Changes to introduce CanWriteResult for Xml OutputFormatters.
Fix abstractions break in tests.
Modify TemplateRenderer to use ThrowIfFaulted instead of Task.Wait
Fixes #782
Change ThrowIfFaulted to WaitAndThrowIfFaulted
Issue #347: Throw a better exception when the user didn't add the MVC services.
Introducing MarkerService for identifying if MvcServices were added.
Remove `using` for Microsoft.AspNet.Mvc.Razor namespace from views
- eventually will clean up IntelliSense -- removing classes users don't
  need when editing a view
- will _not_ cleanup IntelliSense 'til VS stops using a private copy of
  Microsoft.AspNet.Mvc.Razor.Host.dll or we update that copy
- all tests and MVC sample views still work fine
- issue #969
Optimize attribute routing link generation
Optimizing Attribute Routing Link Generation
CR feedback adding tests for implementation
CR feedback