added section field to RWADef (https://github.com/restlet/apispark/issues/1328)

Added the field in RWADef's Resource class, filled it in both Introspectors, moved method getFirstSegment from SwaggerConverter to ReflectUtils as it is now used in Introspector as well.
fixed SwaggerConverter (https://github.com/restlet/apispark/issues/1328)

Added TBO's enhancements on the SwaggerConverter of extension APISpark. Removed condition that kept methods OPTIONS and PATCH to be inserted in RWADef, removed useless NPE protection on apiProduces and apiConsumes and swagOperation#getItems. For the last one, NPE moved to the class ResourceOperationDeclaration.
Refactored code.