Minor build cleanup.
Simplify build solutions logic.
Improvements in MVC Attribute Routing:
1. Flatter attribute hierarchy.
2. Moved template validation outside of the attributes.
3. Main entry point moved to the main namespace for better discoverability.
Add Ok(value) action result.
Cleanup file names.
#1064 Multipart parser not setting content length header on inner contents
MVC Attribute Routing - basic extensibility scenarios
Add NotFound() action result.
Fix performance regression from MVC override filters.
1043: $expand fails when the navigation property being expanded is null.

There are two issues here.

1) If the expanded navigation property is null, we still get it as
SelectExpandWrapper<>. This is because entityframework cannot create nulls
of non-entity types. Fixing this by adding a property to tell if the
expanded property is null for expanded properties.

2) If there is a projection on the expanded navigation property, i.e lets
say $select=Customer/ID&$expand=Customer and Customer is null,
entityframework projects Customer/ID as null and tries to assign it to an
int (as ID is an int). It fails in the materializer. Fixing this by
promoting non-nullable properties to nullable properties in the generated
query if null-propagation is not enabled (EF scenarios).
pacify policheck
Use preferred .NET 4.5 APIs in web host.
Add Created(location, value) action result.
Add BadRequest(message) action result.
Add Json(value, ...) action result.
Add Conflict() action result.
Add Unauthorized(challenges) action result.
Issue 909: Exceptions in DefaultODataPathHandler result in 500
Add InternalServerError(exception) action result.
Add Ok() action result.