Issue #1081 - XML DataContract Formatter can fail to write when instance type != declaredType.

Adding Functional tests appropriately.
Removing XmlSerializerInputFormatter from the list of Formatters.
Introducing a functional test for XmlSerializerInputFormatter.
Issue #1072: Adding Unit Tests for GetSupportedContentTypes, CanWriteResult and for XmlFormatters with DeclaredType as object.
Making UrlHelper's methods virtual
Addressing CR feedback
- Reverted back changes related to adding new virtual methods
- Added documentation to UrlHelper
Addressing CR feedback
Addressing code review feedback
- Fixed comments and moved them to IUrlHelper interface
- Using attribute routing on SimplePoco controller