[mms] Don't log authentication exception messages from the IMAP library; authentication failures are already logged by the authentication code.
Only show success notification if the user can actually add addresses to the safe list

The pref may be locked, for example.
Optimize
[mms] Don't show option to add senders to safe images list if the current address cannot be added to the safe list.
[mms] Fix regression in throwing exceptions when parsing POP3 server responses.