Add support for "data_provenance" metadata

[jameshadfield]

We now support data provenance to be defined in the dataset JSON
(see nextstrain/augur#705) and all core
nCoV builds have been updated to include this here. This commit
parses and renders such information.

Note that a previous commit removed the "Build info" from the byline
for datasets displaying GISAID (this commit), which I believe was an
oversight. This commit reinstates it.

Examples:

 "data_provenance": [
      {
        "name": "GISAID"
      },
      {
        "name": "COG UK",
        "url": "https://www.cogconsortium.uk"
      },
      {},
      {
        "name": "source with invalid link",
        "url": "/bad.link"
      },
      {
        "name": "source without link"
      }
    ],

Rendering of /ncov/global with this PR:

For comparison, rendering of /ncov/global as of v2.24.1 (parent):

[trvrb]

This looks great to me @jameshadfield. Thanks so much for implementing. The link parsing is a nice touch. This is good to go from my perspective.

[huddlej]

This worked for me, exploring the ncov builds in the Heroku deployment. We don't currently link out to GISAID from the button, but there was a comment in the original issue about linking from the given image to GISAID's site. Is that functionality we still want? Should it be in a separate PR, so this most important functionaity can get this out as soon as possible?

[emmahodcroft]

Good catch @huddlej . My expectation is that GISAID would likely prefer if that logo links to their website. But that might take a bit of fiddling, I agree that getting this live first and then working to incorporating the linking would be best, so that other builds can implement this quickly.

[trvrb]

Nice catch! I didn't realize that the link out to gisaid.org was missing from the live version as well. We should make this addition. It won't be hard.

[trvrb]

Okay. This commit adds a link to gisaid.org and will also catch data_provenance.name = gisaid (which seemed like it could be a common input). I think this can be merged now.

[jameshadfield]

Thanks all ⭐