When returning chat boxes via the API.

We can do this now because these API methods are only available to
(whitelisted) plugins.

Otherwise `require('converse-core')` can be called, exposing the inner converse
object.

Much smaller library.
No dependence on jQuery.

Updates #779

This reverts commit e6360722.

Merge branch 'pr/chats_open_attrs' of https://github.com/Ape/converse.js into Ape-pr/chats_open_attrs

Keep the focus in the input after filtering.
Prevent form submission from reloading the page.

According to the require.js docs this shouldn't be done.
http://requirejs.org/docs/whyamd.html#namedmodules

Move styles related to embedded chats to `css/converse-muc-embedded.css`

Don't include muc-embedded by default