Merge pull request #645 in ZP/z-push from bugfix/ZP-1329-z-push-admin-doesn-t-work-on-impersonated-accounts to develop

* commit '7da39ad1':
  ZP-1329 Fixed typos.
  ZP-1329 Removed not necessary else cases.
  ZP-1329 Log impersonated user also in syslog.
  ZP-1329 Send ReplyBack notification email to the authenticated user, as he lacks permissions.
  ZP-1329 Revert IBackend->Logon() change.
  ZP-1329 Revert IBackend->Logon() modifications and remove the $impersonatedUsername to keep backward compatibility. This needs to be redone in ZP-1351.
  ZP-1329 Refactored impersonation feature to a global level.