console: sort task list

[hawkw]

right now, in the top view, it's not possible to sort the tasks by anything --- they are stored in a hashmap, and rendered in iteration order.

we should probably find a nice way to make them sortable, and (eventually) let the user control which key they're sorted by, like in real top(1). it's useful to store the tasks in a hashmap for applying updates, since we can index a particular task and update its stats, or quickly remove them. ideally, we should find a way to sort them without having to copy from the hashmap into a vec every time we render the list of tasks.

one thing we could do is make the actual task data refcounted, the actual task data, and then construct btrees for every sortable parameter as different sorted views of the task list, so that every sort is ready to go when the user selects it...