[uilib] don't print timedeltas between 0 and 23h as negative (closes #2236352)

[storage/bfss] ensure bfss never remove a cw_edited item (closes #2236287) When the <old value> == <new value> (not really and update but can happen), the value was popped but never restored. The cw_edited attribut had wrong content for a small time lapse.