Generator layer, refactors filename methods (#424)

* deprecates toSecurityFilename

* Reduces the number of deprecated method definitions

* Deprecates toContentTypeFilename

* Deprecates toRequestBodyFilename

* Deprecates toHeaderFilename

* Deprecates toPathFilename

* Deprecates toParameterFilename

* Deprecates toOperationFilename

* Deprecates toSecuritySchemeFilename

* deprecates toServerFilename

* Deprecates getSchemaFilename

* Eliminates nulll jsonPath passing into getFilename

Author: spacether