NEXUS-5472: Honoring LocalStatus and ProxyMode

Multiple fixes:
* fixing NPE for offer events if they came in before WL inited (more to come)
* fix to honor local status and proxy mode
* javadoc
NEXUS-5472: If offer/revoke flies in during update of hosted repo

Then we simply respawn the update (which is a cancellable task)
to get the content change into account. Since this is handled
for hosted repositories only, local storage scan is fairly
fast.