Added confirmation upon dashboard user deletion.
Added confirmation upon dashboard user deletion.

refs #4674

michal-ruzicka/archivematica,eckardm/archivematica,sevein/archivematica,artefactual/archivematica,sevein/archivematica,artefactual/archivematica,eckardm/archivematica,michal-ruzicka/archivematica,sevein/archivematica,eckardm/archivematica,artefactual/archivematica,michal-ruzicka/archivematica,eckardm/archivematica,michal-ruzicka/archivematica,artefactual/archivematica,sevein/archivematica