Replace social Auth manager

[fpliger]

The current app registered at google for social auth management it linked to my personal account and points to dev address. Before launch we should:

• register a new proper app under the official europython account (ping @malemburg can you do that?)
• activate the GPlus App auth on that app otherwise it will not work..
• set both the dev.europython.eu, europython.eu and ep2015.europython.eu as redirects
• set the new app auth keys on settings.py

[barrachri]

#60