#3 Removed dependencies on System.Web from the model

I have split the BinaryVersion.Handler into two projects:
- BinaryVersion.Core which has models and doesn't use any features from
.NET 3.5 or higher and so the classes can be reused in projects
targeting different .NET framework versions
- BinaryVersion.Handler still targets .NET 4.5

- Also updated FileVersion - FilePath is private and accessible via a
method, which makes it safely non-serializable. This fixes an issue with
older .NET framework versions that don't have e.g. [ScriptIgnore]
attribute.
- Refactored the code of response objects, so that the concrete
serializer is instantiated closer to the place where it's used and
there's no more need for special classes handling XML or JSON responses.