Refactoring and multiple response_type support

[Ali Aliyev]

As part of this task, I would like to carry out a small refactoring of the project to prepare for the openid integration (See: #26).

TODO List:

• Add multiple response_type support (based on this document: https://openid.net/specs/oauth-v2-multiple-response-types-1_0.html):
  • Add new response_type - none.
  • Add response_mode query parameter.
• Project refactoring
  • Move basic validators from GrantTypeBase, ResponseTypeBase to AuthorizationServer class, create another method validate_request on the AuthorizationServer class level. Also get rid of BaseRequestValidator and move it's validators to the level of the AuthorizationServer class.
  • Rename list_to_scope / scope_to_list to list_to_str / str_to_list, since we need the same helper functions for response_type