Responsive table TODOs

• Fix border radius on separate btn-group buttons
• Add correct role to all table elements (grid, rowheader, etc) - https://gitlab.com/gitlab-org/gitlab-ce/issues/33375
• Fix empty state https://gitlab.com/gitlab-org/gitlab-ce/issues/33376
• Add mobile-only headers to pipeline page
• Add mobile-only headers to environment detail page
• Fix overflow bug