Use $ref from swagger annotation as suggested identifier

[neiser]

The $ref property of swagger annotation as suggested identifier. This is accessible in the following code places (incomplete list):

• DefaultApiResponseAnnotationMapper
• DefaultHeaderAnnotationMapper
• DefaultRequestBodyAnnotationMapper / DefaultRequestBodyOperationCustomizer

The string provided is actually intended to manually reference another item, but I think using it as the suggested identifier is the better usage of that annotation property.

[neiser]

Might be related to #10 and #15