For the MUCJoinView and the LoginPanel

This came out of the desire to let `converse-muc` use the API to
determine whether MUC is supported. However, we don't know the entity
JID before hand and I couldn't think of a good way to query all current
and future entities for a feature.

So `converse-muc` still does it's own thing without the API, but some
refactoring came as a result of attempting.

Let a promise be returned instead of a wrapper, but glue the `resolve`
and `reject` methods onto it

This removes the need for `switch (obj)` in the template which is not
allowed in strict mode.

Additionally using a named variable speeds up rendering.

- Update build scripts to use transpiled versions of newly added modules
- Stop building locales.js and remove locales stuff from build scripts
- No need for Grunt anymore since we don't need to make locales.js

to check whether a certain service discovery feature is supported by an entity.

- Use `enabled` method for plugins
- Rename `converse-inverse.js` to `converse-fullscreen.js` and make it a
  core plugin.
- We're no longer making separate mobile and inverse builds

No longer a need to whitelist/blacklist plugins for inverse to work.

- Adds new config setting: `view_mode`
- `converse-singleton` is now a core plugin and its behavior depends on `view_mode`.

- Also allow private chats to be opened via URL fragment.
- Make sure to clear the URL fragment when the relevant chat is closed.

upon login or after registering.

* Update localisation/translation documentation due to recent changes.
* Remove `moment_locales.js` and instead load the moment locales in `src/i18n.js`
* Mention how to load the fullscreen version. Refs #939

* Translated using Weblate (German)

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/

* Translated using Weblate (Indonesian)

Currently translated at 36.3% (97 of 267 strings)

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

* Translated using Weblate (Indonesian)

Currently translated at 34.0% (91 of 267 strings)

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

* Translated using Weblate (Indonesian)

Currently translated at 32.9% (88 of 267 strings)

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

* Translated using Weblate (Indonesian)

Currently translated at 32.9% (88 of 267 strings)

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

* Translated using Weblate (Indonesian)

Currently translated at 33.7% (90 of 267 strings)

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

* Translated using Weblate (German)

Currently translated at 98.1% (262 of 267 strings)

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

* Translated using Weblate (Norwegian Bokmål)

Currently translated at 72.6% (194 of 267 strings)

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

* Translated using Weblate (German)

Currently translated at 100.0% (283 of 283 strings)

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

* Translated using Weblate (German)

Currently translated at 100.0% (283 of 283 strings)

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

* Translated using Weblate (French)

Currently translated at 92.2% (261 of 283 strings)

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

* Translated using Weblate (French)

Currently translated at 92.5% (262 of 283 strings)

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

* Translated using Weblate (French)

Currently translated at 95.7% (271 of 283 strings)

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

* Translated using Weblate (French)

Currently translated at 96.1% (272 of 283 strings)

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

* Translated using Weblate (French)

Currently translated at 100.0% (283 of 283 strings)

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

* Translated using Weblate (Norwegian Bokmål)

Currently translated at 70.3% (199 of 283 strings)

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

From the perspective of the XMPP server, this is an entirely new login,
and therefore as per RFC-6121 the roster SHOULD be queried, making the
client an "interested resource".

https://tools.ietf.org/html/rfc6121#section-2