Add option to change calendar/list of existing tasks in properties sidebar #97

When I create a task, it will often be created in the wrong calendar. (1)

I then need a way to set the correct calendar for the task. As there is no visible option for doing this in the UI (2), I propose to add this option to the task properties menu.

(1): That is because it is cumbersome and slow to always select the correct calendar on the left menu before adding a new task in the main window. Slow due to the reload of the filtered task list; even with good internet connection it is an annoying delay. Furthermore, i do not like nor need the filtered task list when adding a new task, as i usually go on with adding a task for another calendar.

(2) I discovered just today, after months, that it is possible to use drag and drop. This does not solve my issue because

• it is not intuitive (at least, has not been for me) - there is no indication that the tasks may be reordered
• like for the calandar, there should also be a way to set this as part of the right-hand properties menu.
• in a long list of tasks, distributed over more than 4 calendars, drag&drop does not perform very well.