Allow variant annotation update in case overview

[holtgrewe]

Is your feature request related to a problem? Please describe.
It is very tedious to update already annotated variants: lookup in variant overview, get a search result that includes them, update them in the results table.

Describe the solution you'd like
We need controls to update the variant in the case overview screen (Variant Annotation tab in /variants/{project}/case/{case}/).

Describe alternatives you've considered
N/A

Additional context
N/A

[holtgrewe]

Implementation Proposal
Add buttons to the case variant annotation overview that allow to variant annotation updates in this screen. Ideally, show the forms in modals. Saving the variant should trigger a reload of the variant annotation tab. Reuse as many existing APIs as possible.

Affected Components

• VarFish Server only

Affected Modules/Files

• variants/templates/variants/case/detail_annotation.html

Required Architectural Changes

• None

Implementation Sketch

• Add buttons and modal to HTML
• Add Javascript for the code
• Add tests