This change set builds collectd from source and configures it in one of
the following ways:

- If Librato credentials are present, collectd will be configured to
send data points to Librato using the collectd-librato plugin.

- If no Librato credentials are present, collectd will be configured to
write RRD files locally (/opt/collectd/var/lib/collectd/rrd by default).

added dovecot-pop3d
allowed in the firewall
monitored with monit
added relevant tests

Remove all configuration for MySQL and configure PostgreSQL as the main
database.

All *_mysql_* options have been changed to *_db_* options.

Postgres requires the database user to have a password in order to
connect via localhost. The db_admin_password option is used to set the
password of the admin user (usually postgres).

Web interface listens on localhost only.
The web interface is needed for polling monit
status from the console via::

    monit summary