Latest readings potentially misleading

[oscgonfer]

This issue is to open a discussion on a potential improvement to solve the case mentioned here: https://forum.smartcitizen.me/t/charts-on-the-map-website-not-working/1637

When the kit stops sending data except the battery, the sensors in the kit overview are not updated and the timestamps are mismatched, so it could be misleading as in the forum's post.

I suggest to keep the implementation as is, but maybe highlight the kit overview data that is phased out by a certain time threshold, for instance, data that is 1h or 1day old could be lighter gray.

[oscgonfer]

Adding to this here, it was discussed at some point, but not fully detailed, to change the latest reading to have timestamp per sensor. This would allow us to easily identify if data is old.