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.
Merge pull request #250 from xamarin/split_SILVERLIGHT_defines

Split some SILVERLIGHT flags into separate parts