(ugly fix)

Reduce text size, set text to justify, try to improve readability.

Add ability to add links to headers.

The previous editor was a simple div that had contentEditable set to True and some small js code to create titles, images, center things....

It was too hard to type using this badly-created half-finished wysiwyg editor, so I switched to ParseDown.

Previous posts will render correctly since html code is saved with content in database, and new posts will only save markdown content, and will render to html only in views.

Less clicks, more typing, yay!

add external project link in post infos, replace link in project title

* I forgot to add the cover-related stuff in the ProjectsManager's functions
* I forgot a comma in the sql query in AdminManager

*add preload for 404.css

*add output buffering
*add preload for font & minified.css

*optimize icon.png, mobile-menu-icon & mobile-menu-icon-close.png, and serveur_petit.png
*remove ubuntu-related fonts, now the site use sans-serif and a subset of share tech mono