Classification file attachment cache is not working correctly

https://github.com/windup/windup/blob/master/reporting/api/src/main/java/org/jboss/windup/reporting/service/ClassificationServiceCache.java#L40 doesn't do "retain" on the right thing. It should be on fileModel not classificationmodel.

Also, the cache is a static, when it should really be tied to an execution. Maybe via GraphRewrite?