mono-upnp_moved_to_gitlab

Added DoNotSerialize and DoNotDeserialize attributes to
Mono.Upnp.Xml and unit tests to go with. Decorated Root.UrlBase
with DoNotSerialize.

Reworked the Uri properties in Icon and Service to better handle
the serialization of Url fragments relative to the device
description url.

Added unit tests for serializing and deserializing the device
description information (the Root class). This includes the Dummy*
types and the DeviceDescriptions class which has reference XML.