New horizontal navigation for project pages

• Apply new style to project page https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4053
• Restructure project navigation to have less tabs on 1st level (from 15 to 10). See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4053#note_12005400 and https://gitlab.com/gitlab-org/gitlab-ce/issues/17983