Also improve the introductory text.

Also, the minimized chats view now gets rendered after chat boxes are fetched,
so we need to make it check for already added and minimized chats.

if the `controlbox` is not there.

Also, make `converse-controlbox` and `converse-muc` optional dependencies of
`converse-minimize`.

* ChatRoomView.getDefaultNickName() when muc_nickname_from_jid  is used

Allows to overridde nickname by plugins when muc_nickname_from_jid is used.

* CHANGES.md updated

Refs #909

xgettext doesn't support them yet, which causes errors in the pot/po files.

https://savannah.gnu.org/bugs/?50920

updates #909

* Translated using Weblate (German and French)

Currently translated at 98.4% (260 of 264 strings)

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

* Translated using Weblate (French)

Currently translated at 99.6% (263 of 264 strings)

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

Specifically for IE11.

* Add a polyfill for String.prototype.includes
* Make sure all bundled code is transpiled
* Add IE specific fix in converse-otr.js

Also, declare it in the controlbox plugin, not in core, where it's not used.