Bump to latest backbone.browserStorage which adds the `clear` method

Handle any `error` IQ result or timeout from a MUC ping as indication that we're no longer joined.

Otherwise we might run into a situation where a very old,
cached MUC that's being restored has `connection_status` set to ENTERED
(and the user happens to be in the MUC via another client)
and then restores cached messages without taking
`clear_messages_on_reconnection` into account.

we already listen for `beforeTearDown` and do what's necessary there.

`initStatus` is no longer on the `_converse` object, so the override
wasn't being applied and chat boxes get closed when the
`clearSession` event fires.

It was in any case setting the wrong key, should've been `nick`

We now distinguish more clearly between joining and re-joining a MUC.

The `enterRoom` method has been refactored away.

Instead, `join` or `rejoin` should be used, depending on the circumstances.

Don't fetch cached occupants in the `initialize` function, instead, only fetch
them if we're restoring a MUC that we're still connected to.

If we're not restoring a still-connected MUC, then we clear the
occupants cache, and the messages cache if `clear_messages_on_reconnection` is `true`.

updates #1807
updates #1808

See https://git.happy-dev.fr/startinblox/components/sib-chat/issues/96

Otherwise Converse might only realise we're no longer in the room when
the user tries to interact with it.

* Add screenshot for embedded view mode
* Add Pàdé

- Remove need for the `converse-mouse-events` plugin.
- Register `mousemove` and `mouseup` handlers only when necessary and only inside the MUC DOM element.
- Restore converse-dragresize to roughly it's original state before work started on this.
- Move `applyDragResistance` to utils.

updates #1640

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/