Use php-intl extension to display datetimes a bit more nicely, depending on the locale.
What changes:
* the day is no longer displayed
* day number and month are ordered according to the locale
* the timezone is more readable (UTC+1 instead of CET)
* Add API settings in `configure.html`
* Fix textarea autoresize
* Load user.css from data folder
* Move fold/expand all button to the right and fix an issue with already folded items
* Reset datetime display to international datetime
* Temporarilly remove JS login panel (need improvement and integration with the plugin system)
* Body background is slightly lighter
* Fix an issue where thumbnails were hidden by description
* Fix an issue where private orange bar wasn't displayed with thumbnails
* Remove the gradient bar behind titles
* Fix empty bookmarklet name in Firefox
