New REST API error handler method - MissingRequestHeaderException

[IgorBalog-Eng]

When invoking REST API (offeredResource, and probably others) if required header is not sent, it will throw error and in RESTExceptionHandler class, this will be handled by handleGeneralException, which will result in HTTP status 500.
It should be HTTP status - 400 - bad request.

org.springframework.web.bind.MissingRequestHeaderException: Missing request header 'resource' for method parameter of type URI

When new handler is implemented, update also documentation where we describe behavior of those interfaces.