Frictionless EE installation

Most of our purchases are coming from people starting with EE. The goal is to make it easier for people to start using EE.

**Design action items (Luke + front-end):** 1. On https://about.gitlab.com/installation/ make the 'Omnibus package installation (recommended)' section look the same as the other sections, just 5 logo's. 1. When someone clicks the logo the install instructions for EE using a package server are shown inline. (these do not depend on the version of the operating system) 1. Below the install instructions there are links for: CE, troubleshooting https://docs.gitlab.com/omnibus/ , manual installation. 1. The requirements are moved from the text in /downloads to the top of /installation, it will be a text saying 'GitLab hardware requirements recommend installaing a machine with a least 2GB of memory.
**Other action items:** 1. Both http://about.gitlab.com/downloads and http://about.gitlab.com/downloads-ee redirect to https://about.gitlab.com/installation/ => @joshlambert will do 1. GitLab Runner https://docs.gitlab.com/runner/install/ and the Chinese mirror https://mirror.tuna.tsinghua.edu.cn/help/gitlab-ce/ are added to the installation page under official methods respectively Community installation methods => @joshlambert will do

**Design Mockup:**

Install instructions for EE using a package server are shown inline: