Test generated C# classes for DDI 4.0

[alireza1111]

The build process with https://github.com/colectica/cogs does the code generation.

[borsna]

Generated classes are availible in the beta 3 release:
https://github.com/ddialliance/ddimodel/releases/tag/v4.0-beta.3 (the all outputs)
Test e.g. miltilingual strings, study unit with subjects other cv:s etc

[DanSmith]

These settings are needed when testing the json serialization

JsonConvert.DefaultSettings = () => new JsonSerializerSettings
{
    MetadataPropertyHandling = MetadataPropertyHandling.Ignore,
    DateParseHandling = DateParseHandling.None
};

[alireza1111]

DateConverter DateTimeOffset roundtrip adds +1h.
Reported here.