Remove dependencies on Portable Class Library

Create C# library projects for OxyPlot_NET40 and ExampleLibrary_NET40
Update OxyPlot.AppVeyor.sln to include the two new projects library
Update projects referencing OxplyPlot and ExampleLibrary to handle the NET_40 compatibility
Update the OxyPlot.Core.nuspec to handle .NET4.0 and .NET client profile frameworks version
Remove dependencies on Portable Class Library

- Fix issues due to new csproj using same GUID.
- Missing project configurations in .sln
Update .NET40 csproj
Update OxyPlot.Core.nuspec for NET45
Removed Metro c# project into appVeyor solution file. (Bad merge.)
Removed Metro c# project into appVeyor solution file. (Bad merge.)
Merge pull request #249 from thomsonreuters/NET40.Compatibility

Net40.compatibility