simplify mail status in the CLI

from the CLI, I think we should display only something like:

bitmaskctl mail status
mail: ON
SMTP: running
IMAP: running
UNREAD: 42

or

bitmaskctl mail status
mail: FAILED
SMPT: running
IMAP: FAILED (cannot start service, port is already being used)

so, basically, we can get rid of the error fields.