May need way to indicate data version in about.html

[wu-lee]

Currently, coops UK's map says which version of the data it is using in the about panel.

This text is versioned with the map, and not with the data, nor mykomap.

So it becomes incorrect as soon as the data is updated.

This will be a problem with any map which attempts to say something about the data version in the about box.

Possible solution: about box is a template, with certain placeholders for values like this, when they can be procured from the data (perhaps from meta.json).

But not this may not be enough either: there's currently no way to find out things like "this data is from Co-ops UK Q3 2023" because nothing in the data records this. meta.json just as version numbers of the code used to generate the data, and timestamps.