Makes it possible to show a validation message in a downstream
application.

Allows for using IndexedDB as the persistent store, instead of localStorage

Also, insert occupants sidebar before inserting the chat into the DOM

When restoring an already entered room from cache.
Otherwise we end up with an empty history.

Otherwise we end up with no textarea when rendering a MUC that starts
with connection_status of entered but which then needs to reconnnect.

if we're just going to clear them again

This avoids flashing of messages followed by a spinner.

Currently translated at 88.2% (374 of 424 strings)

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

Currently translated at 93.4% (396 of 424 strings)

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

Currently translated at 100.0% (424 of 424 strings)

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

Currently translated at 35.4% (150 of 424 strings)

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

Currently translated at 100.0% (424 of 424 strings)

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

Currently translated at 100.0% (424 of 424 strings)

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

Currently translated at 70.8% (300 of 424 strings)

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

Currently translated at 100.0% (424 of 424 strings)

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

Currently translated at 82.5% (350 of 424 strings)

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

Currently translated at 72.2% (306 of 424 strings)

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

Currently translated at 76.7% (325 of 424 strings)

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

Currently translated at 100.0% (424 of 424 strings)

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

Currently translated at 100.0% (424 of 424 strings)

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

Currently translated at 100.0% (424 of 424 strings)

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

- Add config variable `muc_show_logs_before_join`
- Restore nickname form for the original use-case (when not showing MAM logs before joining).
- Render nickname form in the `.muc-bottom-panel` when showing MAM logs (instead of in a modal)
- Show a message when there aren't any archived messages to show
- Fix converse-mam so that chat logs are properly fetched before entering a MUC

closes #1266

`streamFeaturesAdded` should only be triggered once we've received them
from the server.

This appears to be a timing bug, likely introduced by the IndexedDB
refactoring.

- Retracted moderated message are not editable
- Use "removed" for user-facing text