Report implementation provenance information

[tidoust]

The implementation status information that gets rendered comes from agglomerating different sources. The specs/impl.json file now contains the provenance information. It would be good to present it to users, e.g. when they hover some browser icon.

As usual, the main difficulty is to find the right way to render the info without cluttering the table.

[tidoust]

An idea might be to link to the source that was used to compute the status, and to create some sort of separate view per feature where we can get more detailed information, including links to other sources.

[tidoust]

Clicking on the browser icon now takes the user to the Platform status source that provided the information. I created #217 to track the creation of a more detailed view.