NEXUS-2834: Original implementation was too eager.

It was kicking in for every file deletion made from anywhere,
clobbing tasks like snap remover that were removing items
in a batch (md was rebuilt for every file removed, even if whole
GAV was about to be deleted). Moreover, tasks like
snap remover DO rebuild MD when done, but in optmized
fashion, see ParentOMatic use et al.
Added since tags
Merge remote-tracking branch 'origin/master' into nexus-2834-rebuild-md-on-ui-actions
Merge remote-tracking branch 'origin/master' into nexus-2834-rebuild-md-on-ui-actions
NEXUS-2834: Adapted IT

as repo-trash folder does not even exists (is lazily created)
after fix.
Merge pull request #52 from sonatype/nexus-2834-rebuild-md-on-ui-actions

NEXUS-2834: rebuild md on ui actions