So that we know an event will be emitted when the stanza is sent.

This is probably fine as a patch release. Even tough files have been
moved around, the API is still the same.

With the recent fixes in backbone.browserStorage, the 'file' attributes
gets persisted to browserStorage before Converse tries to upload the
file.

The File object can't actually be serialized, so an empty map gets
stored and then returned together with a 'change' event.

Instead, store the file as a direct attribute on the message object.

Fixes #1261

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