Reactivated drag in wizard for new content elements

+ Fixed the flickering on hover
+ Hover images will show only, if second source is available
+ CSS compromise between patchset 2 and comments

Change-Id: I2119eaffd04b930f8c3802ae50a32aca775a50df
Resolves: #57462
Reviewed-on: https://review.typo3.org/29177
Reviewed-by: Jo Hasenau
Tested-by: Jo Hasenau