Meta issue for new UI improvements

• Mobile icons https://gitlab.com/gitlab-org/gitlab-ce/issues/19170
• Pin state 1366px https://gitlab.com/gitlab-org/gitlab-ce/issues/19171
• Sidebar Icons https://gitlab.com/gitlab-org/gitlab-ce/issues/18393
• project header https://gitlab.com/gitlab-org/gitlab-ce/issues/18544 - https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4989
• group header https://gitlab.com/gitlab-org/gitlab-ce/issues/19205
• user avatar https://gitlab.com/gitlab-org/gitlab-ce/issues/18543