Draft: jh_issue_5

#5 CC @qianzhangxa

Hi @godfat-gitlab, Can you help review the code, and give some suggestions about refact the code? Thank you.

Update files: app/helpers/appearances_helper.rb, app/helpers/application_helper.rb, app/views/layouts/header/_help_dropdown.html.haml, app/views/shared/_logo_type_jh.svg, app/views/shared/_user_dropdown_contributing_link.html.haml