Timestamps on Created and Modified At Values on Card Comments and History

[kartoffelheinz]

The implemented solution from issue #2818 (closed by #3532) for the cards (tooltip) is great and exactly what was needed, but the implementation forgot to also update the comment and history section.

Especially the comments are in dire need. Getting bitten by this all the time, because there is no way to figure out what e.g. comment made "3 months ago" actually means in terms of date, could be anything between 56 and 92 days from now.... And there are times when you need more than a vague estimate.