Add "Display" dropdown on Organization front page

What does this MR do and why?

Related to #421449 (closed)
Designs: &11187 (closed)

The grouptenant scale team is starting to build out an Organization MVC. For more information about what an "Organization" will be see https://docs.gitlab.com/ee/user/organization/

This MR continues starts building the front page by adding the "Display" dropdown that will be used for the groups and projects list. More progress on the front page to come in &11187 (closed)

UX notes

• In the next MR I will be adding the empty states
• Stats will be added in #421447 (closed)
• The actual project/group lists will be added in #421446 (closed) and #421445 (closed)
• The Organizations::Organization model does not yet support a description so we will be adding that in #422078 (closed)
• Subscriptions will not be part of the MVC so I have left it out of the avatar. Confirmed with PM &11187 (comment 1514168095)

Screenshots or screen recordings

Desktop	Mobile

How to set up and validate locally

1. Open Rails console
   • bin/rails console
2. Enable the feature flag
   • Feature.enable(:ui_for_organizations)
3. Navigate to /-/organizations/default

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.