add code of conduct info. take it from https://github.com/devfest-berlin/code-of-conduct/blob/master/code_of_conduct.md
and from https://github.com/python/pycon-code-of-conduct
modify code of conduct including only info taken from https://github.com/devfest-berlin/code-of-conduct
add favicon.png
it only uses favicon.png
update _config.yml with DevFest Berlin 2014 data. TODO: check