Fix headless build webpack config

so that we can emit an event when sending a stanza.

#1257: Prefer 'probably' over 'maybe' when evaluating Audio support.

- Also update versions in package.json
- Update Makefile

* Update moved dependencies references to @converse/headless
* Remove unused webpack resolve aliases

* Link internal dependencies by relative path
* Don't use webpack aliases for external dependencies to reduce
user-side configuration

Arabic: Currently translated at 82.9% (297 of 358 strings)
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/ar/

Norwegian Bokmål: Currently translated at 62.8% (225 of 358 strings)
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/nb/

French: Currently translated at 98.8% (354 of 358 strings)
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/fr/

Hungarian: Currently translated at 100.0% (358 of 358 strings)
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/hu/

Polish: Currently translated at 80.7% (289 of 358 strings)
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/pl/

Czech: Currently translated at 99.7% (357 of 358 strings)
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/cs/

Romanian: Currently translated at 26.8% (96 of 358 strings)
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/ro/

Spanish: Currently translated at 60.0% (215 of 358 strings)
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/es/

German: Currently translated at 88.2% (316 of 358 strings)
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/de/

Basque: Currently translated at 100.0% (358 of 358 strings)
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/eu/

Japanese: Currently translated at 100.0% (358 of 358 strings)
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/ja/

Convert more promise-based tests to async/await

- Use async/await instead of promises.
- Use different room jids (to try and see whether this fixes heisenbugs on travis)

updates #1209

fixes #1209

updates #1242