- copy over legacy MVC's `SelectExtensions`, `SelectListItem` and `SelectListGroup`
- plus expected `SelectList` and `MultiSelectList`
- fixup select HTML helpers to meet WebFx standards and work in new world
- usual stuff: `[NotNull]`, `var`, `String` -> `string`, long lines, ...
- remove `IDictionary<string, object> htmlAttributes` overloads
- move longest extension method overloads into correct classes / interfaces
- add `ViewDataEvaluator.Eval()` overload for an `object` container
- rename lower-level helpers to make purposes more obvious
- nit: move Raw() methods up from bottom of HtmlHelper.cs
- use `DropDownList[For]()` in MVC sample
The fix here is to do some cleanup we've been planning to do for a while,
rather than flowing IUrlHelper and IComponentHelper as part of the
ViewContext, they now are just grabbed from the service provider.
This simplifies the code for invoking a view, and gets us closer to the
desired API surface of ViewContext