We distinguish between UniView and MultiView instances.
UniView means that only one chat is visible, even though there might be multiple ongoing chats.
MultiView means that multiple chats may be visible simultaneously.
Removed `_converse.chatboxviews.showChat` and trying to simplify how
chats are created and when they're shown.
Prompted by the work to split the MUC views into a separate plugin
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.
- 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.
So that when a room is closed, a previously obscured chat doesn't become
visible again. Allowing this would force us to know which chat is visible, so
that we can falsify it's `hidden` attribute.
