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/

Currently translated at 72.1% (266 of 369 strings)

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

Currently translated at 100.0% (369 of 369 strings)

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