Share in social networks

* Add the social buttons gem to the Gemfile

* Initializer and translations for the social buttons

* Add the social buttons assets to the sprockets require

* Add the social buttons in the show debate view

* Spec to lock down the amount of social share buttons to three

Gemfile.lock

@@ -241,6 +241,9 @@ GEM
       json (~> 1.8)
       simplecov-html (~> 0.10.0)
     simplecov-html (0.10.0)
+    social-share-button (0.1.8)
+      coffee-rails
+      sass-rails
     spring (1.3.6)
     sprockets (3.2.0)
       rack (~> 1.0)
@@ -318,6 +321,7 @@ DEPENDENCIES
   responders
   rspec-rails (~> 3.0)
   sass-rails (~> 5.0)
+  social-share-button
   spring
   turbolinks
   uglifier (>= 1.3.0)