By registering a one-time event handler for a unique event name

After some back-and-forth, I think it's still better to keep markup in
templates (instead of having them directly inside the components)
becaues it makes it easier for people to modify Converse.js (at the
expense of some developer ergonomics).

Bumps [websocket-extensions](https://github.com/faye/websocket-extensions-node) from 0.1.3 to 0.1.4. **This update includes a security fix.**
- [Release notes](https://github.com/faye/websocket-extensions-node/releases)
- [Changelog](https://github.com/faye/websocket-extensions-node/blob/master/CHANGELOG.md)
- [Commits](https://github.com/faye/websocket-extensions-node/compare/0.1.3...0.1.4)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

Bumps [uglify-js](https://github.com/mishoo/UglifyJS2) from 3.8.1 to 3.9.1.
- [Release notes](https://github.com/mishoo/UglifyJS2/releases)
- [Commits](https://github.com/mishoo/UglifyJS2/compare/v3.8.1...v3.9.1)
Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

This is to try and make it clearer that this method won't override
initialization settings, and is instead simply to add to the default
settings.

This is a problem that could occur when calling converse.initialize twice

Credit for this work goes to @deleolajide

Fixes #2040