[BUGFIX] Content Object Loader register wrong class properties

Convert the properties to LowerCaseUnderscored.

Resolves: #60672
Change-Id: Idf99318067a498a07d31a8ef15bd528ac5b46587
Reviewed-on: http://review.typo3.org/32019
Reviewed-by: Tim Lochmüller <tim@fruit-lab.de>
Tested-by: Tim Lochmüller <tim@fruit-lab.de>