Enable 'asterisk' role to submit voicemail object.

1. Adds user role 'asterisk'.
2. Adds 'asterisk' user with 'asterisk' role.
3. Allows 'asterisk' role to submit voicemail object.
4. Updates controllers, models, and views for voicemail.
5. Changes 'callTime' field from timestamp to int(11) in voicemail table.