Allow custom JSON serialization / deserialization settings in JSON plugin

[yozzozo]

Feature request: It would be nice if the JSON plugin supported more of the Json.NET API, such as adding in custom serialization settings.

I know I can just build the plugin myself or use the JsonConvert class myself, but allowing custom settings would be slightly better :)

[slodge]

Originally, the intention of moving this out to a JSON plugin was to make the JSON implementation optional and to make it independent.

This was especially important as there are good reasons for people to sometimes use JSON.Net, sometimes use ServiceStack/Text and sometimes use the official JsonContract thing

This kind of makes the plugin API (IMvxJsonConvert) independent of JSON.Net - and I'm not sure how we could inject settings across multiple JSON implementations...

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With that said.... maybe a new JSON plugin could be built and could implement some Newtonsoft-specific interfaces?

Linking this to #551

[damasojm]

according to yozzozo, it would be great to set some options of json.net