Bump django from 2.2.1 to 2.2.4

Bumps [django](https://github.com/django/django) from 2.2.1 to 2.2.4.
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/2.2.1...2.2.4)
Signed-off-by: dependabot[bot] <support@github.com>

Instead of Sensor Group set to Null, it now is set to the
Miscellaneous group, which is also the default sensor group.

Also added API version endpoint.

Remove unnecessary timeseries chart key deletion for charts with > 20 sensors

 20 sensors.

The default Plotly chart configuration does not contain a 'b' key and
 attempting to remove that key throws an exception which bubbles up to a
 generic error message displayed to end users and no chart.