v2.0.0

• Renamed the Client class to APIClient and ClientConfig to APIConfig for readability.
• The OAuth2Config expects only the url parameter be given in config.
  The necessary paths for different actions will be appended by the SDK.
• Added the locale config parameter to OAuth2Config.
• OAuth2Client::initAuthCodeFlow() now accepts uri which expected to be the full authorization url of auth server
  and nextUri which is the next url to be continued after successful authorization.
• Removed SessionStorage in accordance to the new workflow which doesn't take responsibility of sessions at SDK level.
• SignatureValicator is renamed to SignatureVerifier and expects SignatureGenerator as a dependency.
• Fixed the token cache invalidation issue.
• Bug Fixes.