This PR adds the concept of a global `DrawThread`, which can receive
multiple renderers to draw information on the screen (note: the
underlying thread is released back to tokio when it's not rendering). It
also separates the concept of progress bars from the existing "draw
thread". This makes it trivial for us to do stuff like show permission
prompts and progress bars at the same time in the future.
The reason this is global is because the process' tty stderr is also a
global concept.
