[#2] added search form in header, fixed problem with i18n
[#3] Added 'angular_rails_csrf' gem
[#3] Added 'sessions' controller, 'login page', added 'authorization', 'principal' services - authenticate users, added 'social-buttons-3' CSS
[#3] Added 'roar-rails' gem, created user head representer and added it to head
[#2] Added logout button when logged in, added user first_name on header when logged in
[#3] Added login errors as 'bootstrap alerts'