Include a Mastodon link besides the user name below post titles

We show the Mastodon URL alongside the website URL and XMPP address.
This crowds the user box even more and I think LinuxFR should switch to
using a proper profile page instead.

This was requested by Adrien Dorsaz.

Author: nud

app/helpers/node_helper.rb

@@ -111,6 +111,7 @@ def posted_by(content, user_link='Anonyme')
       user_infos = []
       user_infos << homesite_link(user)
       user_infos << jabber_link(user)
+      user_infos << mastodon_link(user)
       user_infos.compact!
       user_link += (" (" + user_infos.join(', ') + ")").html_safe  if user_infos.any?
     end

app/helpers/users_helper.rb

@@ -40,4 +40,8 @@ def jabber_link(user)
     link_to("adresse XMPP", "xmpp:" + user.jabber_id)
   end
 
+  def mastodon_link(user)
+    return if user.mastodon_url.blank?
+    link_to("Mastodon", user.mastodon_url)
+  end
 end