Completely restored authorization_code grant for user side.

Reworked oauth_sessions table.
Added extension to use MariaDB's JSON columns.
Rewritten tests for authorization_code grant for client side.
Deprecate some old shit.
[skip ci]

api/exceptions/ThisShouldNotHappenException.php

@@ -7,6 +7,8 @@ namespace api\exceptions;
  * The exception can be used for cases where the outcome doesn't seem to be expected,
  * but can theoretically happen. The goal is to capture these areas and refine the logic
  * if such situations do occur.
+ *
+ * @deprecated use \Webmozart\Assert\Assert to ensure, that action has been successfully performed
  */
 class ThisShouldNotHappenException extends Exception {