Added Showdown to render Markdown

**Story URL:** [REACT-TASK-5](http://facebook.github.io/react/docs/tutorial.html)
**Project:** Zadar
**Reference person:** [me]
**Description:**
Showdown library to render Markdown

 * [x] Add the third-party Showdown library to application
 * [x] Convert props to string and render by html (using dangerouslySetInnerHTML)

**Migrations:** No
**Rollback:** No
**New dependancies:** None
**Manual actions:** None