upload limits: show how upload limits are calculated in profiles.

* Allow mousing over the upload limit on profile pages to show the full
  formula for the upload limit calculation. In particular, show how the
  upload limit multiplier is derived from the deletion confidence.

* Refactor to avoid duplicating upload limit calculations in the
  presenter, as much as possible.

app/presenters/user_presenter.rb

@@ -68,13 +68,14 @@ class UserPresenter
       return "none"
     end
 
-    dcon = [user.deletion_confidence(60), 15].min
-    multiplier = (1 - (dcon / 15.0))
-    max_count = [(user.base_upload_limit * multiplier).ceil, 5].max
-    uploaded_count = Post.for_user(user.id).where("created_at >= ?", 24.hours.ago).count
-    uploaded_comic_count = Post.for_user(user.id).tag_match("comic").where("created_at >= ?", 24.hours.ago).count / 3
+    limit_tooltip = <<-EOS.strip_heredoc
+      Base: #{user.base_upload_limit}
+      Del. Rate: #{"%.2f" % user.adjusted_deletion_confidence}
+      Multiplier: (1 - (#{"%.2f" % user.adjusted_deletion_confidence} / 15)) = #{user.upload_limit_multiplier}
+      Upload Limit: #{user.base_upload_limit} * #{"%.2f" % user.upload_limit_multiplier} = #{user.max_upload_limit}
+    EOS
 
-    "(#{user.base_upload_limit} * #{'%0.2f' % multiplier}) - #{uploaded_count - uploaded_comic_count} = #{user.upload_limit}"
+    %{#{user.used_upload_slots} / <abbr title="#{limit_tooltip}">#{user.upload_limit}</abbr>}.html_safe
   end
 
   def uploads