Split some SILVERLIGHT flags into separate parts

**LIMITED_CONSOLE** to remove access to `Console.OutputEncoding/Color/BufferLength`
**NO_STRONGNAME_SIGNER** to remove strong name signing
**NO_NATIVE_RESOURCES** removes the linking of native resources, (this
never happens on mono anyway)
**NO_WIN32_REGISTRY** remove access to Microsoft.Win32.Registry
**NO_SYSTEM_CONFIG** removes access to System.Configuration

This allows component parts to be applied rather than the whole
**SILVERLIGHT** set of flags.  This is very useful for building FCS in
constrained environments like Andoid etc.