1. Add a new `view_mode` value: `embedded`.

   This value is used to determine wether the `converse-muc-embedded`
   plugin is active or not.

2. Remove the need for the #converse-embedded-chat element.

   Instead we reuse the #conversejs element and embed inside that.

3. Removed the need to manually blacklist core plugins

   This is now done automatically if `view_mode` is set to `embedded`.
   Perhaps eventually we don't blacklist at all and instead use the
   `enable` plugin method. For some that probably won't work, like
   `converse-chatview`, which we still need to be active.

Setting it on `window` is necessary to have it available inside a
webcomponent.

Triggering an event is necessary so that we don't call
`converse.initialize` too early.

Needed when converse.js is included inside a webcomponent.
The fonts.css file is then copied over to the host DOM.

Necessary due to this bug:
  https://bugs.chromium.org/p/chromium/issues/detail?id=336876

We have bedroom, bathroom, classroom and boardroom as one word.
Living room is spelled separately because of the present participle (+ing) in living.

With "chatbox" it's a bit more subjective.
We have chatbot as one word (but litter box as two).
For consistency with chatroom, I'll go with one word.

which we check by checking if the PEP identity is provided.
https://xmpp.org/extensions/xep-0163.html#support

Also, the condition was the opposite of what it should have been.

Appeared to only complicate things...