Obsolete fixes

[Hertzole]

Fixes some obsolete warnings in newer Unity versions and generally future-proofs the package while maintaining backwards compatibility.

• Replaces AppDomian.CurrentDomain.GetAssemblies() with Unity's new way of getting loaded assemblies in Unity 6.4+
• Removes FindObjectsSortMode usage in Unity 6.4 as it's obsolete
• Mark PredictedIdentity.id as NonSerialized to stop Unity from complaining about trying to serialize it

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