added list of sections to contract, removed section from Resource (https://github.com/restlet/apispark/issues/1328)
added javadoc on Contract.sections (https://github.com/restlet/apispark/issues/1328)
corrected errors in Introspector and SwaggerConverter caused by disappearing of field Resource.section (https://github.com/restlet/apispark/issues/1328)
added field description in Section, updated SwwaggerConverter so that it takes Sections into account during RWADef=> Swagger conversion (https://github.com/restlet/apispark/issues/1328)
added NPE on Contract#getSections() (https://github.com/restlet/apispark/issues/1328)
fixed formatting, updated SwaggerConverter, Section, Contract in Swagger ext, deleted obsolete attribute section in Resource (https://github.com/restlet/apispark/issues/1328)