[IMP] website: media editor doubleclick for video and begin to use snippet builder

addons/website/static/src/css/editor.css

addons/website/static/src/css/editor.sass

addons/website/static/src/css/website.css

addons/website/static/src/css/website.sass

addons/website/static/src/js/website.editor.js

addons/website/static/src/js/website.snippets.animation.js

addons/website/static/src/js/website.snippets.editor.js

addons/website/static/src/xml/website.editor.xml

addons/website/views/snippets.xml