Change API response data structure.

[andrey-helldar]

For errors:
From: {"error":{"error_code":400,"error_msg":"Test message"}}
To: {"error":{"code":400,"msg":"Test message"}}

For success:
From: {"response":"Text message"}
To single information: {"Test message"}
To a few items: {"count":0,"items":["Test message 1","Test message 2","Test message 3"]}

[andrey-helldar]

Upgraded:

For errors:
From: {"error":{"error_code":400,"error_msg":"Test message"}}
To: {"error":{"code":400,"msg":"Test message"}}

For success:
From: {"response":"Text message"}
To: {"Test message"}