Revert "[TASK] Migrate to ExtJS 4: Replace the ExtJS Skin"

This reverts commit 62f27741.

Change-Id: I1c4ea0153f08b7430c510f3b1b9afceedb64712c
Resolves: #33164
Releases: 4.7
Reviewed-on: http://review.typo3.org/7775
Reviewed-by: Oliver Hader
Tested-by: Oliver Hader