[TASK] RTE: Add to skin css and image required by jQuery UI Resizable

Releases: master
Resolves: #63758
Change-Id: I880002fcc6c2b9e5f44f67e6ab838486d4e4726a
Reviewed-on: http://review.typo3.org/35280
Reviewed-by: Stanislas Rolland <typo3@sjbr.ca>
Tested-by: Stanislas Rolland <typo3@sjbr.ca>