Sidebar navigation

This MR changes layout of the GitLab to sidebar navigation.

Layouts:

- [x] Project layout
- [x] Project settings layout
- [x] Dashboard layout
- [x] Profile layout
- [x] Group layout
- [x] Snippets layout
- [x] Admin layout

Pages:

- [x] Activity pages
- [x] Issue/mr pages
- [x] Issues/merge requests pages

Common:

- [x] Fix tests

See merge request !1329