Fix terminal newlines

[edlerd]

Done

• terminal was messy with newlines before due to race conditions on incoming messages through the websocket. Treating the messages as arraybuffer avoids the race
• show prompt on tab or browser close, when user interacted with the terminal, this avoids accidental terminal closing. Before we'd only prompt on navigation, not on close.

Fixes #537

QA

1. Run the LXD-UI:
   • On the demo server via the link posted by @webteam-app below. This is only available for PRs created by collaborators of the repo. Ask @lorumic or @edlerd for access.
   • With a local copy of this branch, run as described here.
2. Perform the following QA steps:
   • test the instance terminal. The newline bug could be reproduced by just keeping enter pressed to force a lot of new lines. This was reproducible for me only in firefox, not in chrome. This should now produce stable newlines
   • test the instance terminal prompt on tab close or reload. It should show a prompt when interacted with the terminal.

Screenshots

Before broken terminal with newlines in wrong places due to a race condition:

Fixed terminal with stable newlines:

[webteam-app]

Demo starting at https://lxd-ui-547.demos.haus