Byte Pack Convert - Networked GameObject, Component, GameResource References (#1618) * Add add IBytePackConvert to a class to specify how it should be serialized/deserialized with BytePack (similar to IJsonConvert). Implement for GameObject. * Add IBytePackConvert support to Component and GameResource * We should be able to null these out * Some comments on ConverterPacker to describe its use * Let's move it out of Sandbox and call it BytePack.ISerializer - it won't be exposed to public API (for now?) * Makes sense to rename to SerializerPacker so it matches ISerializer * Explicit implementations of BytePackRead and BytePackWrite means we can have these non-public * Add test for BytePack.ISerializer with MySerializedClass * Some minor doc change * Tidy