Canvases in the order of your choice

The canvases can now be put in any order in the configuration: each one has an up and a down arrow beside its name, like the tasks in the queue. Once saved, the new order applies at once, without a restart, to every list of canvases: the canvas switcher in the bar and the canvas picker on the phone. The order is kept in the configuration file, so it holds after a restart.