cli: multi workflow commands

[oliver-sanders]

Provide a nicer representation for multi-workflow commands.

Could do something Tui-style (but also colour coded) along the lines of:

$ cylc stop one two tre fou
⊚ one
● two
⊗ tre
  Error: Workflow does not exist

Consider also #3329 which should allow commands to yield a stream of messages/updates to the client, providing updates on the requested action. The intention is to do something like this (interactive mode only):

$ cylc stop one
(Ctrl+D to run in background)
● Connecting to workflow
⊚ Waiting for active tasks to complete

Combining the two:

$ cylc stop one two tre
(Ctrl+D to run in background)
⊚ one
  ● Connecting to workflow
  ⊚ Waiting for active tasks to complete
● two
  ● Connecting to workflow
  ● Waiting for active tasks to complete
⊗ tre
  ⊗ Connecting to workflow
  Error: Workflow does not exist

We can't use Urwid for this as it needs to take control over the whole terminal, however, it should be easy enough to achieve using plain old ANSI (colorama allows us to move the cursor up and down, left and right). Otherwise can use the built-in curses.

Pull requests welcome!