Show date along the X axis on the conformance chart

[jasonwilliams]

Looking at the graph on https://boa-dev.github.io/boa/test262/# its not easy to know what time the test represent. It would be nice to show the years along the bottom or something to know how far back these results are showing.

Example below:

Looking at the data it seems only the commit is stored, so for backdating we may need to run a script which returns the datetime for each commit. Each item in that JSON should also have an ISO date field for past and future additions

[jedel1043]

We no longer have a conformance chart, so that should be implemented first.