EventJournalProcessor isn't properly handling ignorable events (like those caused by HCM itself)

There are several problems and bugs with the current event handling in EventJournalProcessor:

•  uses the wrong session (eventProcessorSession) to save the lastRevision in case all events turn out to be ignorable (causing the change not to be persisted, yet)
• events generated by HCM itself (at startup), except for only the first time startup, are not ignored either, causing for example every (new) content definition to be exported immediately again
• known ignorable derived properties (like hippo:paths) are not ignored, causing unnecessary attempts to detect changes