there is in general too many article/section where we just need normal div

see http://html5doctor.com/the-section-element/ for more information.

Basically, we'll use a section (or article) if you'd have a header for the section. Otherwise, just use a div.
Use an article when it's something that is consistent by itself (see http://www.whatwg.org/specs/web-apps/current-work/multipage/sections.html#the-article-element for more information about this)

Here, I'd use div for everything, maybe a section for "composer-container" but that's all