Handle groups in hit extraction view.

[njohner]

With this PR we add the possibility to select groups to define the included and excluded genomes in the hit extraction view.

Because this makes displaying the possible choices more difficult, we delegate this to the backend by introducing the django autocomplete light package. This package will use Ajax requests to ask the backend for updated lists of available choices, depending on other fields in the form. We therefore add two new views responsible for providing the choices for selecting genomes and for selecting the number of Missing data allowed.

I'm not quite sure how selecting groups should behave when "Distinguish plasmids from chromosomes" is enabled. For now, selecting a group will select the corresponding taxons but not the plasmids.

Checklist

• Changelog entry
• Check that tests still pass
• Add tests for new features and regression tests for bugfixes whenever possible.