Separate continous integration results, doxygen documentation and emscripten demos

[BrunoLevy]

Continuous integration results, doxygen documentation and emscripten demos are generated in gh-pages, this makes the size of the repository grow considerably (especially continuous integration results). For now, continuous integration results is configured to wipe out gh-pages history, but this wipes out doxygen and emscripten demos as well.
Find a way of sending them to separate repo.