* ui: fix websocket connections on dev proxy
`ember-cli` includes a handler for websocket upgrade requests to start
proxying requests. Handling the same upgrade event by also proxying in
`api.js` causes some kind of conflict where the connection is closed
unexpectedly.
The only change necessary on upgrade is to overwrite the Origin header
so Nomad accepts the connection.
* ui: remove unused variables
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.
