[BUGFIX] Make element browser work again

Due to the cleanup of the DocumentTemplate
html variants, the Element Browser did not
work as a <body> tag is now rendered.

The solution is to only fetch the
<html> and <head> part from the
PageRenderer and build the frameset part.

Resolves: #62825
Resolves: #62345
Releases: master
Change-Id: Id267e1e9b79c000f17e52a60901602002c13d45a
Reviewed-on: http://review.typo3.org/33948
Reviewed-by: Stefan Froemken <froemken@gmail.com>
Tested-by: Stefan Froemken <froemken@gmail.com>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>