Add generic OAuth consumer data related logic.

Remove over complicated DropboxAppOAuthData class.
Add OAuthConsumerDataValidator class to replace the DropboxAppOAuthData functionality in a more generic and simpler fashion.
Add contract OAuthConsumerDataSource for consumer data source implementations.
Add contract OAuthConsumerDataValidator for consumer data validation implementations.
Add tests for OAuthConsumerData.
Add OAuthConsumerDataNGTest data providers class.
Add OAuthConsumerDataNGTest testing data wrapper DTO class.
Add multiple package Javadocs.