Improve how seqDetails page displays per-segment metadata

[corneliusroemer]

We currently treat per-segment metadata like any other metadata on seqDetails page (and elsewhere on the website).

We are thus throwing away intrinsic structure and making the seqDetails page overwhelming (CCHF has 3 segments, for flu with 8 it'd be even more overwhelming).

We can group in two ways: top level being field name or top level being segment. I think I'd prefer top level being segment. Reason is that if you look at for example per segment QC metadata, you study one particular segment and look at multiple fields rather than looking at a metadata field across segments.

Increase in per-segment metadata fields comes with: #2108

Example of current state (once #2108 is merged):

[rneher]

One could have a tabbed view like we have for the sequences below with segment specific metadata. This would also allow to not show (missing) data for missing segments.

likewise, instead of length 0 we could show something like -- in the browse table.

[corneliusroemer]

Alternatively, we could show each segment's stats under its own header (in its own box, like INSDC, Sample details etc). And only show headers for segments that are present.

[anna-parker]

Closing as #2316 resolved issues with grouping segments under one header and removing blank spaces. Work to improve the sequence view will be followed in #2376