Add new XML plugin support

[SamuraiCrow]

XML serialization plugin now available! We should support it!

[SamuraiCrow]

After having looked in greater detail at the XML plugin, its applicability might be limited to importing existing RapaGUI XML files into the editor. The existing XML recursive output might benefit also but maybe to a lesser degree.

[SamuraiCrow]

This will likely benefit from Hollywood 10.