Tomtoolkit

This release fixes the following:

- Completes the upgrade to the ALeRCE v1 API.
- Updates the TNS API URL to the updated value.
- Adds ``DEFAULT_AUTO_FIELD`` to ``settings.tmpl`` for new TOMs. Existing TOMs should add ``DEFAULT_AUTO_FIELD = 'django.db.models.AutoField'`` to their ``settings.py``, which will resolve any warning messages that include ``HINT: Configure the DEFAULT_AUTO_FIELD setting``, provided the existing TOM is on Django 3.2 or later.

This release removes the MPC module as a default, given that the latest version of astroquery has an issue with it that will be fixed in the next release.

Users of the MPC should follow the instructions listed [here](https://tom-toolkit.readthedocs.io/en/stable/api/tom_catalogs/harvesters.html#minor-planet-center) in order to ensure that it works.

This release includes most, but not all, of the upgrade to the new ALeRCE API. It should be considered to be in beta as long as the disclaimer at the top of the ALeRCE query form is present.

This release supercedes the mistaken 2.6.1 release and includes the fix for spectroscopic migration alluded to in 2.6.1. It also includes a stub module for the Fink broker.

This release contains the following:

- Refactors user_list to use templatetags in order to facilitate introduction of new [tom_registration](https://github.com/TOMToolkit/tom_registration) installable app.
- Adds django-rest-framework API endpoint for cancelling observations.
- Adds support for assigning group permissions to observations submitted via the django-rest-framework API endpoint.
- Upgrades ``numpy``, ``astropy``, and ``astroplan``, and removes support for Python 3.6.

What to watch out for

- HTML in ``user_list.html`` has been replaced by templatetags, so anyone overriding the ``user_list.html`` template should copy the changes. They can be reviewed in [this pull request](https://github.com/TOMToolkit/tom_base/pull/430/files).
- HTML for login buttons in ``base.html`` has been replaced by a templatetag. Changes can be reviewed in the above pull request.
- Support for Python 3.6 has been removed.