ANN: Better display of points in time - easily switch between relative and absolute

[williamstein]

Points in time are displayed all over in CoCalc, e.g., when a file was last modified in the file explorer, when a change occurred in TimeTravel, and the log of key events in a project. Sometimes its useful to show those times relative to now, e.g., "3 weeks ago", and other times you want to see the exact time, e.g., "2/27/2023, 7:03:27 PM" or even the ISO time "2023-02-28T03:03:27.685Z". It's now very easy to switch between these different modes, and also see and copy paste times.

• Click on the time to see a popover (no automatic hover)
• The popover looks the same for either relative or absolute mode, and provides both times, and also the ISO timestamp.
• You can always copy the times since the popover doesn't automatically close (until you click somewhere else)
• You can easily toggle between showing all times in relative or absolute mode at any time without having to go to account settings.