[TASK] Streamline TS registration for sysexts

For historical reasons the "Static Template #43"
was "content.default" and the possibility to add
TypoScript after this default rendering was introduced
in order to have CTypes and plugins register their
TypoScript just after e.g. "content.default" or
"css_styled_content".

Since TYPO3 CMS 6.2 the preferred option is
called "defaultContentRendering" instead of
the magic number "43".

Some leftover parts in sysexts are replaced
with "defaultContentRendering", as well
as some more descriptive information on
how the legacy number exists.

Releases: master
Resolves: #65346
Change-Id: I7268ec9ee8454d1eb4b0fda9f12fdfb5cb191ba8
Reviewed-on: http://review.typo3.org/37239


Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>