nicer block for oauth signin links

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/devise/sessions/_oauth_providers.html.haml

 - providers = (enabled_oauth_providers - [:ldap])
 - if providers.present?
-  %div.light-well{:'data-no-turbolink' => 'data-no-turbolink'}
+  .bs-callout.bs-callout-info{:'data-no-turbolink' => 'data-no-turbolink'}
     %span Sign in with:  
     - providers.each do |provider|
       %span