Update (or, more correctly, create) the changelog in the process.

We now have common Python project CI templates which, while continuing
to support PyPI publication, also allow for parallel matrix testing with
tox.

The GitLab CI configuration in this repo dates from a time before this
feature was in GitLab (as noted in the comments) and so had to work
around it by creating a lot of templated jobs.

Simplify the CI configuration by making use of the common template.

Downgrade required version of ucam-identitylib and be more permissive about required versions

See merge request !2

This is not ideal, but given that we only need the identifiers from identitylib
the downgrade in version and more permission version allows us to use this
library with libraries which are making use of different versions of identitylib
without needing to upgrade identitylib and refactor.

Initial implementation

See merge request !1