Enable deletion of partial intervals/ranges

[xeruf]

Somewhat related to #257, I would like to have a simple way to delete part of an interval - e.g. if I took a break.

I think the most intuitive way would be to allow delete to take a range, e.g.

timew delete 1400 - 1430

This would automatically split the intervals at either end if necessary

The ways I see to currently do it is to either track a temporary interval with the :adjust hint and then delete that, or split two times and then delete the interval in between.

[lauft]

Sounds like a good idea, but maybe there should be some safeguards (e.g. confirmation dialog) installed... 🤔

[xeruf]

As suggested in my PR, I think we should have different behavior depending on the changes - if a whole interval is deleted vs only its times changed: #329 (comment)

I would suggest that the delete operation automatically functions like the "adjust" hint I described there.

[xeruf]

To update this: I think such a delete operation with a time should use the conflict resolution we are establishing in #373 by default.