Rename converse-core.js to core.js

Allows 3rd party plugins to add more buttons to the message actions dropdown

Set passed-in properties on modal

* Calculate proper length for :geo URI matches
* Don't strip out line-break after quotes, instead use CSS `display: inline-block`

Otherwise if an endpoint was passed in with `converse.initialize`, then
that endpoint's protocol is (wrongly) used.

to determine valid characters to form a boundary before an `@` mention

Also fixed an issue with mentions looking like they're part of URLs, by
first processing mentions separately.

This reverts commit e0088a45.

since the DOM element breaks the line already

Fixes #1083

Directives are rendered as templates and their bodies are MessageText instances.
We thereby achieve the necessary nesting of directives (and other rich
elements inside directives) by letting each directive
body render itself similarly to how the whole message body is rendered.

Test mention inside a /me message

Currently translated at 100.0% (505 of 505 strings)

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

Currently translated at 71.4% (361 of 505 strings)

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

Newly opened headline chat isn't hidden by default in fullscreen view

Also include some CSS fixes for fullscreen headlines boxes