Backend monitor and overview

[nonhermitian]

Fixes #994

Summary

These are Jupyter magics that gives the overview of all the backends that have been loaded using IBMQ.load_accounts() (backend_overview) or a detailed view of a single backend (backend_monitor). The backend_overview updates automatically, while the monitor is currently static. Additionally, there is a plot_coupling_map function in the visualization module.

Overview

Monitor

Details and comments

Things to do:

• The coupling map drawer needs a better way of handling the required equal aspect ratio.
• The figure size used in the monitor is hacked (backend specific) because of the above issue.
• The coupling map drawer should probably be moved elsewhere as its usefulness goes beyond this PR.
• Need to verify that the upper bound on the pending jobs correctly extends itself if the number of jobs goes above the default 50.
• The background function update_backend_info should gracefully handle a status check not working, and should probably terminate if none of the backends are responding (i.e there is no network connection to anything).(Each backend_widget has a is_alive attr, added just for this purpose)
• Allow for changing the status check interval via a magic arg.
• The mpl_data is the physical layout of a device on a grid. This should be something that the backend returns.
• Make the damn linter happy.

[jaygambetta]

man @nonhermitian were you watching this in real time.