Avoid `An 'url' property must be specified` error by properly clearing
presence data upon teardown and then resetting the browserStorage upon
reconnection.

Store contact resources in a Backbone collection

* Add test and changelog entry
* Also show message subject if available

Changes:

* Avoids leaky abstraction of MUC code into converse-chatboxes
* Avoid creating unnecessary message objects (e.g. without <body)
* Add fix for #1369.
* Rename spec/chatroom.js to spec/muc.js

Last comma  forbidden in JSON, example doesn't work as is.

This asks screen readers to read every message received, and is
mandatory for blind users to get notified of new messages.

- Set correct default value
- Set proper Makefile recipe dependency
- Fix rendering issue in changelog

Currently translated at 84.8% (313 of 369 strings)

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

By ditching jquery and using async/await

Fixes #1334

Fixes half of #1337.

Causes the register form to overflow the parent bounds in overlay view

Otherwise we get an empty collection of features (due to features being
queried for a non-existent MUC)

No code relies on this currently, but it's seems the right thing to do

Also, handle the error in `getRoomFeatures`

As a namespacing mechanism to avoid clashes.
Fixes bug where two chats are shown as currently being active in the rooms list.

Causes problems with some versions of Ejabberd which use a different id.
Will be fixed in upcoming versions.

Currently translated at 99.7% (368 of 369 strings)

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

Currently translated at 100.0% (369 of 369 strings)

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

Currently translated at 100.0% (369 of 369 strings)

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

Currently translated at 100.0% (369 of 369 strings)

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