Extract EE specific files/lines for Platform app/helpers

We have the following files containing EE specific code. We should move them to ee/

• app/helpers/appearances_helper.rb
• app/helpers/application_helper.rb
• app/helpers/button_helper.rb
• app/helpers/dropdowns_helper.rb
• app/helpers/namespaces_helper.rb
• app/helpers/selects_helper.rb
• app/helpers/services_helper.rb
• app/helpers/tab_helper.rb