Add missing relation types items in schema global variables
Some of these global variables are used, in particular, to control schema
views (web/views/schema.py).
While they are currently not properly documented (see #3360868), their
definition are currently incomplete (e.g. one could reasonably expect to find
``cw_schema`` in ``SYSTEM_RTYPES``).
Closes #3486114.
addressbook
basket
blog
book
calendar
comment
company
email
file
folder
i18ncontent
keyword
link
mailinglist
person
tag
timeseries
vcsfile