A11Y: Show focus state visibly

[trm217]

⚠️ **contains issues that are also mentioned in #136.

Wait for #136 to be resolved and check what has already been solved.**

Description

Autofocus

For modals and other elements that open in a different place in the dom hierarchy the auto-focus must be set programatically.

Make focus visible

https://www.w3.org/TR/WCAG20/#understandable
https://www.w3.org/TR/WCAG20/#consistent-behavior

Todo

• Videos cannot be focused

• Unselected payment options are not focusable

• Auto focus Audio Player when starting a track (Befund 47 & 52)

• Focused actionbar item must be visible selected

• Auto focus must be set when the series-overview overlay is opened in an article.

• Modals must be autofocus when opened (will require changes in Styleguide)

• Autofocus image light-box