Clean up Install page

Link to review the changes: https://1346-update-install-page.about.gitlab.com/installation/

Updates install page to:

• Unify on a single Docker install page, which directs to hub.docker.com images.
• Update Docker install page to include Docker Store images. Blocked by https://gitlab.com/gitlab-org/omnibus-gitlab/issues/2325
• Change GDK subtext "Runs with a single make command" to "For contributing to GitLab"
• Add Chef logo to GitLab Omnibus Cookbook
• Update Pivotal Tile to include PCF logo, and title of "GitLab Pivotal Tile"
• Complete "card" should be clickable, not just logo or title.
• Add Google Cloud (https://gitlab.com/gitlab-com/www-gitlab-com/issues/1326) Blocked by https://gitlab.com/gitlab-org/omnibus-gitlab/issues/2326
• Below official install section have a section 'Other official methods' with three icons (Upgrade, GDK, GitLab.com)
• Add Juju Install Option

Closes #1346 (closed)