Unify courses and raw materials

Currently, we have two ways to access course materials. The link "Materiály", leading to /courses/, and the link "Kurzy", leading to /runs/. The overlap in their contents is significant and bound to result in confusion. The individual pages for lessons are also duplicated, for instance:

http://naucse.python.cz/lessons/beginners/cmdline/
http://naucse.python.cz/2017/pyladies-praha-jaro/beginners/cmdline/

These pages are templated differently, with the latter having an (arguably) nicer style with a custom font. It also gives a way to go to the next lesson.

These two ways to access lessons should be unified. My approach would be to turn the raw, online-first materials into special (canonical) runs.