Variant page speedup (in particular for actions such as comment, classify and dismiss)

[dnil]

Is your feature request related to a problem in the current program to new available techology or software? Please describe and add links/citations if appropriate.
The variant page takes some time to load, and especially when using several notation fields on the page, it reloads each time to update the page. Noted by in particular @NicoleCMMS.

Describe the solution you'd like
Find speedups: e.g. including some form of cached or js delayed/promise (api call) matching causatives check, cached or delay/promise loqusdb lookup. In particular the latter seems rather doable, as it is via api already.

Describe alternatives you've considered
One could have a mechanism for disabling matching causatives check until asked for, but on the variant level I fear it may be unused and we miss variants. One could also consider more projections on the variant page. And one could consider async/api-call actions from the page, not requiring reloads but instead updating relevant fields. This is a larger operation for comments, perhaps fairly doable for the different label/classification/dismiss dropdowns. A complication is the difficulty in communicating operation completion to the user in a reasonable fashion.

Additional context
Add any other context or screenshots about the feature request here.