Add configurable about this dataset links

[seve]

This PR introduces configurable link outs to additional information about the dataset. These links are featured conditionally in place of the dataset name in the top-left corner and in the info menu in the top-right.

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This PR implements the following changes:

• Server
  • cli/launch.py
    • Add --about flag and description
    • Add link validator and raise an exception if fails
    • Pass the link to config
  • app/rest_api/rest.py
    • add links field to config JSON
• Client
  • globals
    • add empty default for links
  • informationMenu component
  • Add a conditionally rendered menu item
  • menubar component
    • pass about link as prop to info menu
  • TopLeftLogoAndTitle component
    • Conditionally turn the dataset name into a link

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This PR will close #902

[liaprins-czi]

This looks great to me! Thanks for getting this in so quickly! One tiny thing I'd change is the info button link from Title Case to just Sentence case (make "this" and "dataset" lowercase, but keep "About" capitalized).

[seve]

Should note that I haven't added any styles and haven't put much thought into the icon for the menu item. I'm open to any suggestion for the two.

[seve]

@bkmartinjr Could you review the server-side of this PR? This is my first time touching that codebase.

[bkmartinjr]

@seve - please fix the build fail (due to lint added to the Python code). See the Travis error output: server/cli/launch.py:98:1: E304 blank lines found after function decorator.

You can run this on your own box by running the same commands Travis runs. See the .travis.yml file. In this case, I believe flake8 is erroring.

[bkmartinjr]

Several items I recommend changing:

• fix the lint (build failure)
• change "link" to "url", as that is much more accurate
• (optional) improve the URL validation to check for HTTP scheme
• remove the unused flask template variable

See inline comments.

[colinmegill]

The alignment of this dataset title looks correct, baseline aligned with cellxgene

[seve]

Is this compared to the issue we were seeing in #909?

[seve]

You marked requesting changed, but not sure what needs changing

[bkmartinjr]

@seve - you will need to resolve the merge conflict before this PR can be approved.