Implement top navigation for profile area

Main idea is to keep left sidebar static so user is not confused by
changing context. Instead we put changing navigation with changing
content in one main block. I used profile area as a simplest way to 
implement and test this concept. Your feedback is welcome in comments

For https://gitlab.com/gitlab-org/gitlab-ce/issues/14354#note_4878536Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !3824