add omniauth gem
fix readme coveralls link
add facebook omniauth authorization
Merge branch 'develop' of https://github.com/kaize/itc73 into feature/social_networks_authorization_#68

Conflicts:
	app/models/user.rb
	app/views/web/sessions/_sign_in.html.haml
	config/locales/ru.yml
Merge branch 'feature/social_networks_authorization_#68' into develop