RFC: interactive dashboard (work in progress!)

Hi, This is the on-going work in the interactive dashboard. You can run it externally from vivian (configure the line 20, variable host). The dasboard requires installing urwid.

As expected, there are some known problems and TODOs:

• screen is updated every 2 seconds, this breaks keyboard usage. The best solution is updating every second and remove keyboard support.
• it's not possible to set the timeout for discovery (default is 150 secs)
• Do we need a cancel discovery button :?
• Do we want to be able to turn off a port and remove machines? For example, when discovery fails
• better error handling when a machine doesn't have assigned a PDU/port_id. Right now the dashboard won't run and show a message asking to update mars_db.yml

Finally, this MR isn't against branch master because I'm having problems with the latest changes there and didn't want to spend a lot of time debugging it since I'm changing work laptop next week \o/