Describe the bug

Tabs can't be selected and switched using the keyboard alone.
This would help to comply with W3C's web accessibility initiative.

To Reproduce

Use the tab key to move through focusable objects on a page containing sphinx-tabs. Tab sets can't be selected or changed to show content on other tabs.

Expected behavior

Users should be able to highlight and switch tabs using the keyboard.
This behaviour is exhibited by sphinx-panels tabbed content, where the tab key can be used to select the tab set and arrow keys can be used to switch tab.