Also:

* converted two docstrings into JSDoc format
* Don't use `_.isNull`

can cause messages to not appear.

* Check against null not Element.
* Avoid iterating over non-Element nodes

Lately we've been fetching messages only after entering the MUC, so that
we already have occupants to attach to them (due to `fetchMembers` being
called before) and thereby avoid rerenders.

I've now moved message fetching into the `initialize` method and added
missing event handlers for attaching/removing the occupant from a
message as it comes online or goes offline.

We still avoid (some) rerenders because we fetch and wait for cached
occupants before fetching cached messages and we wait for `fetchMembers`
before triggering `enteredNewRoom` which causes MAM messages to be
fetched.

Also fix scrolling bug

We want to fetch messages from cache only once. For one-on-one chats
this is the case because messages are fetched only in the `initialize`
method.

This used to be the case for MUCs as well, until we added the option
`clear_messages_on_reconnection`.

Now we only fetch messages after the user has entered the MUC.

By this time the cached messages are not yet fetched, causing the entire
MAM archive to be queried.

* converse-muc: Handle timeout while fetching affiliation list
* converse-omemo: Handle IQ timeout

in which you can set user affiliations and roles.

Also, let getAffiliationList return an Error instead of `null` if you're
not allowed to fetch a particular affiliation list.

Currently translated at 69.0% (271 of 393 strings)

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

Currently translated at 94.9% (373 of 393 strings)

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

Currently translated at 95.9% (377 of 393 strings)

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

Set converse-profile as dependency of converse-omemo

Don't remove affiliation for occupants if we weren't allowed to
fetch that particular affiliation list.

Previously, if fetching the list failed, we would return an empty array,
which would imply that the affiliation list is empty and that all
users with the given affiliation should have their affiliations removed.

Instead we now return `null` and properly account for that when setting
affiliations on existing contacts based on the returned member lists.

We don't remove the existing chatboxes and upon refetching they
become stale and get removed (by Backbone) and then the UI for
them becomes unresponsive.

Don't remove cached presences in `afterTearDown` event.
We might reconnect again and resume the session, in which case we need
that data still.

Instead, we remove cached presences when `clearSession` fires, because
then we know we're not reconnecting.

When reconnecting, we don't fetch presences from cache, we still have
them (since we no longer remove them in `afterTearDown`).

When reconnecting and not resuming, we clear the presences from cache,
since we're starting a new session.

Translated using Weblate (Chinese (Simplified))
Currently translated at 41.8% (158 of 378 strings)
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/zh_Hans/

Translated using Weblate (Russian)
Currently translated at 96.8% (366 of 378 strings)
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/ru/

Added translation using Weblate (Occitan)
Translated using Weblate (Occitan)
Currently translated at 79.9% (302 of 378 strings)
Translate-URL: https://hosted.weblate.org/projects/conversejs/translations/oc/