fixes #421

updates #1069

Trying to use more generic CSS selectors and to extract out common patterns.

Currently we can only show the room info modal for open rooms, because
we need the Backbone.Model.

Querying the room info and displaying it for non-open rooms will be more
work and will require a separate modal.

when removing offline users who are no longer on the member lists

Highlight the currently open groupchat in the sidebar (in singleton mode).

Currently translated at 79.2% (252 of 318 strings)

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

Our handler was too restrictive due to the namespace matching.
When joining a room and the room's remote server can not be found, then
the resulting error messages doesn't not have the MUC namespace.

Currently translated at 84.3% (264 of 313 strings)

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

* Allow for shift-enter to insert newlines

See issue #1081

* Update CHANGES.md

Currently translated at 83.3% (261 of 313 strings)

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

Currently translated at 83.3% (261 of 313 strings)

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