Improve `HtmlHelper` extension points
- address all of #659 and a bit of #874 (avoid `public virtual` methods in
  `HtmlHelper`)

- make `MetadataProvider` and `GetClientValidationRules()` `public` and
  therefore available to extension methods
- remove unused `GetValidationAttributes()` overload
- make remaining `GetValidationAttributes()` overload (and not
  `GetClientValidationRules()`) `virtual`, allowing derived classes to
  change the attributes without overriding all callers
- reverse `GetValidationAttributes()` and `GetClientValidationRules()`
  parameter order to match precedence
- add `GenerateName()` and `GenerateValidationSummary()` to make
  `protected virtual` method names consistent
- `Name()`, `ValidationSummary()` and `TextArea()` are no longer `virtual`
  because `protected virtual Generate*()` methods exist for all
Make longest `@Html.DisplayForModel()` overload an extension method
- consistent with @Html.EditorForModel()` overloads
Return a copy of the route values in functional tests.

This is a workaround for a Json.Net + CoreCLR issue.
Changing GetLibraryExport to GetAllExports
Adding TextPlainFormatter to always handle returning strings as text\plain format.

Conflicts:
	src/Microsoft.AspNet.Mvc.Common/Encodings.cs
	src/Microsoft.AspNet.Mvc.Core/Formatters/JsonOutputFormatter.cs
	src/Microsoft.AspNet.Mvc/MvcOptionsSetup.cs
	test/Microsoft.AspNet.Mvc.Core.Test/ActionResults/ObjectContentResultTests.cs
	test/Microsoft.AspNet.Mvc.Test/MvcOptionSetupTest.cs
Stylecop fixes
Added Logging to Mvc
`@Html.DisplayName()`, `.DisplayText()`, `.Id()`, `.Name()`, `.Value()` return `string`
- fixes #566 and part of #847
- allows compositions such as `@Html.Label("property", Html.Id("property"))`
  and `@Html.Raw(Html.DisplayText("property"))` (this one is not recommended)
- adjust XML comments to match
- add missing XML comments to `HtmlHelperValueExtensions`
- nit: `TInnerModel` -> `TModelItem`

- increase XML comment consistency for changed methods
 - generally make wording more consistent e.g. how we use words such as
   "returns"
 - use `<see langref="string|true|false|null"/>` more
Remove useless `.ToString()` calls in tests
Add `HtmlHelperDisplayTextTest` and `HtmlHelperValueExtensionsTest` classes
Move web site projects back where they belong
- solution corrupted in a recent checkin
Remove HTML helpers with `IDictionary<string, object>` parameters
- see line 2 of #874
- focus on `TextBox[For]()` and `ValidationSummary()`

related fixes included here:
- `TextArea[For]()` documentation incorrectly indicated their `htmlAttributes` parameters were dictionaries
- handle `htmlAttributes` parameters more consistently; create a dictionary only when necessary
Fix for issue #349
WIP
Fixed ViewContext writers
Added primitive expressions to TagHelpers
WIP