Visualize BCD features that still need to be handled

[tidoust]

This was discussed in last week's WebDX meeting.

The idea would be to create a burndown chart with the number of BCD features that still need to be addressed.

Other metrics raised during the discussion that may be worth tracking and visualizing:

• The number of new features added to BCD, since that's a growing target
• Can I Use key coverage, noting that Can I Use keys that are somewhat arbitrary may never be covered in web-features, on purpose.
• The list of BCD entries that are going to turn "Baseline high" this year.
• Possibly the list of BCD entries that are going to turn "Baseline low" this year, but that's more guesswork.
• Some measure of the usefulness of group features created in web-features.

I also note that the ability to explore features that are not in web-features was raised in #536 (comment). This could perhaps be part of this tooling/visualization as well.

[tidoust]

Another suggestion inspired from #536 (comment) would be to create another burndown chart with the list and number of features already in web-features that don't yet have a status.baseline field.