New plugin features & code refactorization

Three sides for this new release :

1. Raccoon classes refactorization
2. A new manifest format accepted : .yaml
3. Some new features like :
   • a PHP constant for theme namespace
   • enable SVG files in the WordPress media library
   • enable an All options page in the admin dashboard
   • enable a JS detection script using a .no-js class in the body element and a small vanilla JS script in the footer