Add collectd to the monitoring suite

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).
Merge pull request #254 from hectcastro/hc-collectd

Merge pull request #254
Add IRC channel to README
Fix dspam user parameter and data paths. fixes #196
Set `smtpd_relay_restrictions` to backwards compatible mode. Resolves #231.
Upgrade ZNC to 1.4
Put ZNC web interface on its on port that is inaccessible through the firewall
Merge remote-tracking branch 'upstream/master'