even if the global configuration is to disallow it.
* When parsing, include all media URLs, not just the ones from allowed domains.
That makes it possible to change allowed domains on-the-fly,
while still allowing media in individual messages to be shown manually
(via the message actions dropdown).
* Merge `embed_audio`, `embed_video` and `show_images_inline` into `render_media`
* Create new config settings for allowable domains for images, video and audio
* Check the URL domain against a whitelist for the message actions dropdown
If set to a positive integer, the chat history will be kept to that size
by removing older messages.
This happens as new messages come in (as long as the chat isn't scrolled up)
and when the user scrolls down.
Also add the `pruning_behavior` setting
