wikimedia_domains: add more domains, per OTRS db

mchenry currently accepts anything for which it's listed as an MX. This,
in combination with the OTRS router which does a MySQL lookup means
there's more domains that we serve than just the ones we have aliases
for. A careful SELECT + exim4 -bt on mchenry revealed a bit more,
namely wikimedia.com & wikipedia.com.

Add these two, plus reorder the list and add comments so that future
users know what these are for.

Note that the following domains were also found on that list:
  wikilovesmonuments.be
  wikilovesmonuments.cat
  wikilovesmonuments.eu
  wikilovesmonuments.nl
  wikilovesmonuments.org
These are not added, as they were not added by us and are not under our
control. As these point to mchenry, and is impossible for us to change
that, they're going to break anyway, so don't add them to this list yet,
as this should come via an RT request. This really proves why implicit
domain acceptance based on MX records others control is a bad practice
that we are right to abolish :)

Change-Id: I1d220ee9895bfcec15fb00abe6021ff5c381897e