Added some more more to the SocialJsonObject class

- Added constructor taking the JsonObject as it's only parameter. I usually forget to set the property, so now I have to call the constructor.
- Added ShouldSerializeJsonObject() method to play nice with JSON.net
- Added ToJson() and and SaveJson() methods. These methods have until now been implemented individually in each class, but with the introduction of the SocialJsonObject class, it makes most sence to move them here
A lot of changes to fully incorporate SocialJsonObject + some cleanup

- Removed unused imports in a lot of classes
- Removed ParseMultiple(JsonArray) method some a lot of classes since the same logic is available in the JsonArray class