PT51359223: Voicemail notification medium format attach png

- attach pngs only when Full format used
- use audio/mpeg for mp3 attachments
PT48390337 - SQA error log messages in sipXproxy.log

Lowered the log level of two frequent messages logged when the SQA
agent closes the connection of a client. This is a expected behavior
and not an unexpected error.
Merge branch 'release-4.6' into LDAP
PT-39858631 Disabled users in LDAP PT-39858653

-I made disable users task being optional (new checkbox added in admin settings page)