Show seconds when editing a time entry's start or end time

[tanius]

Currently, a time entry's duration is measured with a precision of seconds, but editing its start or end time can only be done with a precision of minutes because no seconds field is shown when editing.

This has for example the effect that one cannot edit a time entry to be exactly 30 minutes long, because it is not possible to change the seconds fields which are usually non-zero.

[jansorg]

Workaround: „Edit“ in the context menu of an item should allow to edit seconds and milliseconds, I think.