Add migration for fixing 1) a dummy RFC entry, 2) three stand-alone

RFCs that didn't get their doc.type set, 3) a big bunch of historic
stand-alone RFCs that have doc.group=None - set these to the
individual submission "none" group for the time being so the view code
doesn't have to deal with a special case.

In some cases this is wrong since there actually was a WG associated
but unfortunately fixing them properly requires detective work
(probably parsing the RFCs) and in at least some cases recreating
historic WGs. In case someone ends up doing this, the documents to
check can still be found with

Document.objects.filter(name__startswith="rfc", group__type="individ")

since there are almost no new RFCs that didn't went through the I-D
process.
 - Legacy-Id: 5284

Author: OleLaursen