Commented Task: Migrate JavascriptSerializer to Newtonsoft.Json [1852]

Use Json.Net (newtonsoft) instead of javascript serializer to improve performances and code clarity.
Comments: Associated with changeset 34440: Version 0.9.0.0
- Implemented a TokenCreator in Tweetinvi namespace as a static class to generate credentials
- Implemented Credentials Accessor to allow developers to access the current credentials of the thread
- Updated LoggedUser to allow requests to be performed from its personnal credentials
- Created TokenCreatorController to use the new design
- Implemented ApplicationCredentials
- Implemented ConsumerCredentials that contains only the credentials information of a consumer
- Tested LoggedUser to verify that the actions are performed with the right credentials
- Removed Token, old TokenCreator, TokenCredentials
- Removed helpers to get DTO objects from Json