This closes#7454. It makes use of the existing watchable tools to
allow the exec popup sidebar to be live-updating. It also adds
alphabetic sorting of task groups and tasks.
This connects Xterm.js to a Nomad exec websocket so people
can interact on clients via live sessions. There are buttons on
job, allocation, task group, and task detail pages that open a
popup that lets them edit their shell command and start a
session.
More is to come, as recorded in issues.