Issue: GREG-66

Issue: GREG-36

- Takes OrgReg url and api key as arguments
- Assumes that the OrgReg api has been registered behind a Gravitee
  instance.
- Introduces active and deleted fields to OrganizationalUnit for
  keeping track of status in OrgReg. Logic should be introduced in the
  future to ensure that Sponsors and Guests are not connected to
  deleted or inactive OUs.
- Add search and orgreg_id to Admin interface of OUs.

Issue: GREG-35

Omits the test folder since checking coverage of the test functions
themselves makes little sense.

Pytest understands unittest-styled tests, so there is no immediate
need to update the test files themselves to a pytest idiomatic
syntax.

Fixes: GREG-14

We use black, the uncompromising Python code formatter.  This means
we have no need for autopep8.

Fixes: GREG-16

Use black to check if the code is well-formatted and fail if it is not.

Fixes: GREG-16

Apparently pka-context-manager is mirrored on UiB's GitLab instance.
Picking it up from there makes a great deal of sense, otherwise the
CI test pipeline will fail because it does not have access to USIT's
Bitbucket instance.

Fixes: GREG-15

Fixes: GREG-15

Fixes: GREG-15

Python 3.9 has some minor library API changes that it would be
useful for us to have, such as type hinting for generics in
collections, union operators for dicts, and perhaps most generally
useful, new methods for removing prefixes and suffixes from strings.

Unless we have a strong reason not to, we should be targetting the
latest stable release.

Fixes: GREG-13