Fix #101 delete slivers.
Fix #101 delete slivers.

An appropriate message was already shown. Added logging of the delete
so that it shows up in the logs and messages table. Also disabled the
"failed" message if no aggregates "failed".

charliemeyer/geni-portal,tcmitchell/geni-portal,charliemeyer/geni-portal,tcmitchell/geni-portal,tcmitchell/geni-portal,tcmitchell/geni-portal,tcmitchell/geni-portal,charliemeyer/geni-portal,charliemeyer/geni-portal,charliemeyer/geni-portal