Currently translated at 82.5% (280 of 339 strings)

Translation: Converse.js/Translations
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/pl/

Currently translated at 84.6% (287 of 339 strings)

Translation: Converse.js/Translations
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/ar/

Also udpate markup to not use `<source>`.

updates #1189

updates #1220

Fixes #1220

* Add support for webm video and m4a audio media files
* updated CHANGES.md

They're no longer needed since we're using webpack

Silently set status when it comes from a presence stanza

Otherwise the private chatbox header doesn't show in Firefox

Update to Strophe 1.2.16

They're not included in the repo and this makes it more difficult for
people to try Converse locally

Previously the Promise.all made it all-or-nothing, now it'll return
partial matches as well and it'll also log error stanzas.

Also fix if/boolean bug when checking whether we should automatically
register