Clear OData classes out of System.Net.Http and System.Web.Http
- Allow side-by-side use of all v3 / v4 extension methods and classes we previously injected into these namespaces

Move extension methods to System.Web.Http.OData.Extensions and System.Web.OData.Extensions
- Rename these methods to let users referencing the v3 assembly continue using them as extension methods
- Make most HttpRequestMessage extension methods properties of a new HttpRequestMessageProperties class
- Leave old locations in v3 assembly for binary compatibility but deprecate them to help users find the new locations

Narrow scope of a few internal extension methods
- Move RemoveRange to ODataFormattingAttribute (otherwise unused)
- Move one CreateErrorResponse overload to ODataActionSelector (otherwise unused)

Type forward SingleResult and SingleResult<T> to System.Web.Http.dll
- Currently special-cased only in OData [EnableQuery] scenarios but could be used elsewhere

Move remaining classes in System.Net.Http and System.Web.Http to System.Web.Http.OData and system.Web.OData
- Rename QueryableAttribute (the remaining public class) to EnableQueryAttribute

Other cleanup
- Run Remove and Sort Usings power tool, touching a few otherwise-unchanged files
- Remove implementations of MediaTypeFormatterCollection extension methods (moved to System.Web.Http.dll in earlier change)
- Improve wording of XML Comments, especially in EnableQueryAttribute and HttpRequestMessageExtensions
- Wrap to shorten long lines