ready2go: Websockets with live task updates

[nrotstan]

Note: this feature has been implemented, but not yet submitted as a PR

• Add initial support for websockets to both the front-end and back-end using socket.io-client and flask-socketio (with eventlet), respectively
• Replace regular front-end polling of task data with use of websockets that immediately communicate task data updates (task statuses, user locks, etc.) to interested front-end clients as they occur, significantly reducing overall network traffic and server load
• Integration is presently limited to listening for task data updates in project.controller and does not replace other occurrences of polling in TM (such as polling for new notifications)

Additional Notes

• While the websockets will work as-is in development, proper support for websockets in a production environment will likely require changes to the hosting environment, such as to the web server configuration, and possibly the addition of message-queue software (redis can work). The flask-socketio docs have an informative section on deploying websockets that is recommended reading

• While websockets are very well supported by browsers these days, socket.io will nonetheless automatically fall back to its own built-in polling mechanism if websockets can't be used by a particular client for whatever reason. Even when this occurs, the socket.io polling mechanism is likely to be more efficient and performant, due to how it works, than the explicit task-status polling that would be replaced

[pantierra]

Thanks for the issue, @nrotstan. I would like to ping @ethan-nelson here, as he has started to make his head around websockets, too.

[ethan-nelson]

Complementary to this issue, we have #1368 filed that implements a differential update for intermediate refreshes of the project. So, in the interim (and for cases where hosts do not want to use the websockets in the future), there should hopefully be some relief for projects with a heavy server load caused by complex geometries and high traffic.