Removes 'hidden-xs' class from user_avatar helper in order for it to be...

Removes 'hidden-xs' class from user_avatar helper in order for it to be visible in environments list.
Allows a class as an option to keep the hidden avatar behaviour in all the places it is needed.

app/helpers/avatars_helper.rb

@@ -4,15 +4,18 @@ module AvatarsHelper
       user: commit_or_event.author,
       user_name: commit_or_event.author_name,
       user_email: commit_or_event.author_email,
+      css_class: 'hidden-xs'
     }))
   end
 
   def user_avatar(options = {})
     avatar_size = options[:size] || 16
     user_name = options[:user].try(:name) || options[:user_name]
+    css_class = options[:css_class] || ''
+    
     avatar = image_tag(
       avatar_icon(options[:user] || options[:user_email], avatar_size),
-      class: "avatar has-tooltip hidden-xs s#{avatar_size}",
+      class: "avatar has-tooltip s#{avatar_size} #{css_class}",
       alt: "#{user_name}'s avatar",
       title: user_name,
       data: { container: 'body' }