finish create issue with milestone and assignee

conf/locale/locale_en-US.ini

@@ -376,6 +376,8 @@ issues.new.clear_milestone = Clear milestone
 issues.new.open_milestone = Open Milestones
 issues.new.closed_milestone = Closed Milestones
 issues.new.assignee = Assignee
+issues.new.clear_assignee = Clear assignee
+issues.new.no_assignee = No assignee
 issues.create = Create Issue
 issues.new_label = New Label
 issues.new_label_placeholder = Label name...