Use relative instead of absolute datetimes

[zusorio]

Currently, whenever we show datetimes in the frontend, we use one of two rather long formats:

• Thu, 05 Sep 2024 15:06:31
• 9/5/2024 at 03:06 PM

A lot of these could be replaced with relative dates like:

• 4 hours ago
• 2 days ago

For general use, a relative timestamp is easier to understand and more relevant. When hovering over these, we could still show the exact date and time.