We now have uniform avatar rendering for the profile, messages and
chatboxes.

By rendering as canvas, we can avoid stretching the image.

In the process I also moved the ChatBoxViews collection into its own
plugin `converse-chatboxviews` and placed the AvatarAware views there.

fixes #1157

Fixes #497

Otherwise we don't include it in the stanza.
So if an error occurs, remove the bookmark again.

So that the chatboxes get closed/removed.

Also, don't render the login form when we're just reconnecting.

after 10 seconds.