Make tabs of AppTabs container focusable to allow keyboard navigation

[dweymouth]

Checklist

• I have searched the issue tracker for open issues that relate to the same feature, before opening a new one.
• This issue only relates to a single feature. I will open new issues for any other features.

Is your feature request related to a problem?

It is currently impossible (as far as I can tell) to activate the different tabs in an AppTabs container with the keyboard.

Is it possible to construct a solution with the existing API?

Not without a heavily extended/customized AppTabs container

Describe the solution you'd like to see.

The individual tabs should be focusable to allow for keyboard control. Space bar should activate the focused tab, and arrow keys as well as the usual Tab / Shift+Tab should move the focus from one to the next once one of the doctabs has focus.

[Jacalz]

This is sounds like a great idea