Function move_event 

pub(crate) fn move_event(
    qt: &CxxQtThread<Sioul>,
    shared: &Arc<Shared>,
    key: &str,
    start: i64,
    new_start: i64,
    new_end: i64,
    only_this: bool,
) -> String

An event moved by a drag in the agenda: its occurrence starting at start now from new_start to new_end (Unix seconds), that time alone or every time (agenda::moved); then sent, the agenda and the plan made again, and “Undo” offered for ten seconds, which writes back what the file held, unless it changed since (a sync, another device). Returns what went wrong, else “”.