Also expand and fix the associated test.

By doing so we create a new DiscoEntity for the room, which allows us to
query for features via the disco API.

We also avoid duplication of functionality between converse-muc and
converse-disco

Also add new API methods which return features and XEP-128 fields.

- Move `getDefaultNickName` to the model and rename to `getDefaultNick`
- Let `checkForReservedNick` return a promise and save `nick` once received
- Updated `openAndEnterChatRoom` to wait appropriately and remove presence-wrapper
- Update tests to wait appropriately
- Remove presence-wrapper in `getRoomFeatures`

See https://xmpp.org/extensions/xep-0045.html#register

As soon as a chatroom from that domain is opened and if the MUC supports it.

Looks like Chromium strips the forward slash from `<br/>` when printing
innerHTML.

Currently translated at 75.5% (256 of 339 strings)

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

Currently translated at 65.7% (223 of 339 strings)

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

Currently translated at 100.0% (339 of 339 strings)

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

Currently translated at 100.0% (339 of 339 strings)

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

- Avoid registering `sendChatState` twice as handler.
- Avoid sending out a CSN right after sending out a message

Don't included MAM data form if there's nothing to filter