All DOM nodes of the CSS class "removeIfDocumentRenderedInFrame" are
removed from the DOM tree on DOMContentLoaded using JS.

We use this to hide/remove the <header> and <footer> from HTML pages
if they are rendered within a frame, for example an <iframe>.

Without this, our error pages look ugly and confusing in some
circumstances (for example, if /uv/uv.html is missing for some reason).

Signed-off-by: Pascal Ernster <pascal.ernster@rub.de>