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
- move `DynamicObject` derivation up to new `DynamicViewData` class, fixing [WebFx-169](http://projectk-tc:8080/browse/WEBFX-169)
- avoid direct `_data` lookup in previous `TryGetMember()`, fixing [#118](https://github.com/aspnet/WebFx/issues/118)
- rename ViewData -> ViewDataDictionary
Also
- flesh out `IDictionary<string, object>` implementation in `ViewData`
- provide `ViewData` copy constructor that allows TModel to change
- remove `TryGetIndex()` and `TrySetIndex()` implementations; use `ViewData[]` instead
- restore `ViewContext.ViewBag` from legacy MVC
Ryan Nowak
Pranav K
N. Taylor Mullen
dougbu