Merge pull request #5 from purban/email_notification

Email notification
Fixing an issue with in?() throwing an exception
Updating the rails_admin.fr.yml file
Adding links to github and maintainer
Adding Simon and Sylvain as new talk mail recipients
Fixing the TalkMailer#new_talk template name
Adding dotenv for development environment
Using an async worker to send new talk notification
Adding a lineup boolean on talks