PCL updates:
- Add Pcl projects for all platforms
- Generator.Detect is removed for PCL build
- Rename *.Pcl.dll to *.dll, and output to BuildOutput\Pcl\$(Configuration)
- Use .NET 4.5 reflection api's, and update TypeHelper to provide needed api's for .NET 4.0 build
- Remove obsolete WeakEventHandler
- Update Eto.Json - Pcl to a PCL assembly so it can be used by Eto.Test - Pcl
- Remove CheckBox.IsChecked, and instead fix the PropertyBinding when converting to a nullable type
- Remove superfluous configurations from PCL solution files
- EmbeddedAssemblyLoader is now included directly into the assemblies that needs it (Windows, Wpf) from Source\Shared folder
- Most flags removed from OperatingSystemPlatform for PCL (e.g. IsMac/IsLinux/IsUnix/etc)