Remove ICloneable and ISerializable from default namespace

[dejx]

After few hours of debugging the Error Message: System.Runtime.Serialization.SerializationException : Type 'xxx' is not marked as serializable.

I found that the problem is in PdfSharpCore

There are few interfaces with default namespaces e.g. https://github.com/ststeiger/PdfSharpCore/blob/master/PdfSharpCore/SilverlightInternals/AgHacks.cs#L55 https://github.com/ststeiger/PdfSharpCore/blob/master/PdfSharpCore/SilverlightInternals/AgHacks.cs#L61

This mean that default namespace is used (System)

This also means, when you include this package to your project, SerializableAttribute is used from PdfSharpCore assembly and not the framework's. Resulting in the error mentioned above.

Please, remove those interfaces.

clone of https://github.com/ststeiger/PdfSharpCore/issues/102