* Slightly improve the media experience
- Use a grid to display the list of media
- Add icons for non-image media preview
- Paginate the gallery
- Add links to the gallery in the editor and in the profile settings to make it more discoverable when you need it
Fixes#432
* Allow video and audio tags in SafeString
Otherwise we can't display their preview, nor show them in articles
Also show controls by default for these two elements
* Show fallback images for audio and unknown files, to make them more visible
* Add a new constructor to SafeString when the input is trusted and doesn't need to be escaped.
And use it to generate media previews.
* Make it possible to insert video/audio in articles
