fix contact persons select field in backend module; add selectbox to select all

git-svn-id: https://svn.typo3.org/TYPO3v4/Extensions/slub_events/trunk@83754 735d13b6-9817-0410-8766-e36946ffe9aa
released 1.1.8

git-svn-id: https://svn.typo3.org/TYPO3v4/Extensions/slub_events/trunk@83755 735d13b6-9817-0410-8766-e36946ffe9aa