Refactor accounts-api

[Annushkaaaaa]

We will migrate account-api to iam-api
To do it easier, we should:

• Rename bad named variables
• Remove all 'ActionResult' returning types
• Fix style code with new .editorconfig file from real-world example
• Remove unnecessary interfaces
• Check, that all unit-tests exist
• Change endpoint url's structure
• Remove duplicated code