Changes to make the code work with 2 pcl profiles

Based on the csproj changes the following was done:
- Add a "GetTypeInfo" fo the .NET4 code, which simply returns the type
itself - this has the effect that many reflection methods can work in
both profiles as many methods and properties of Type just wandered over
to TypeInfo.
- Since the code is still predominantly a .NET 4 codebase, numerous
extension methods wereadded to the .NET 4.5 code base which mimick those
reflection methods that exist in .NET4. These can be found in
TypeExtensions.NET45
- The assembly loading had to be diverged to the assembly loader as
there was a basic incompatibility. That class exists twice and the right
one is added through msbuild.