Leveraging sshx

[nrybowski]

sshx allows opening interactive and collaborative ssh sessions in browsers.

This could replace / enhance the current solution requiring students to open terminals.

To avoid the introduction of a depedency on an external service, INGInious instances should also host the service allowing remote connection.

As the link of an interactive session is easily shareable, access restriction should be implemented to ensure that the expected student performs its exercise.