Support destroy command

[braheezy]

This is more complicated than other commands because it radically changes the state of the Ecosystem. At a minimum, the machine list must be reduced (and redrawn). If that was the last machine in the environment, the vagrant global-status --prune will no longer report the project existence. That means Violet loses access to it and a tab would have to be dropped.

It would be nice to keep the environment and machine(s) in Violet while Violet is running. They would take on the "not started" status, which implies the only command supported is "up", so the logic on what commands are allowed to be run would need updating.