Filter by issues/merge requests without a milestone

Closes internal https://dev.gitlab.org/gitlab/gitlabhq/issues/2372

app/finders/issuable_finder.rb

@@ -10,7 +10,7 @@
#     state: 'open' or 'closed' or 'all'
#     group_id: integer
#     project_id: integer
-#     milestone_id: integer
+#     milestone_title: string
#     assignee_id: integer
#     search: string
#     label_name: string
@@ -76,7 +76,7 @@ class IssuableFinder
return @milestones if defined?(@milestones)
@milestones =
-      if milestones? && params[:milestone_title] != NONE
+      if milestones? && params[:milestone_title] != Milestone::None.title
Milestone.where(title: params[:milestone_title])
else
nil