[TYPO3-dam] dam_ttcontent: Use TYPO3 4.3 Hook tt_content_drawItem instead of XCLASS tx_cms_layout

[Michael Birchler]

Currently dam_ttcontent xclasses tx_cms_layout.php. This causes various 
of problems. TYPO3 4.3 interdouced a new hook for preview images.

See http://bugs.typo3.org/view.php?id=13641 for patch

Michael