Fixed: #2739 beforeDelete funktioniert nicht, #3001 Report: delete implementieren

Index.rst, Constants.php: reverted parameter '_table' in delete links back to 'table' - Reason: 'form' needs to be 'form' (instead of '_form') due to many used places already.
Sip.php: move SIP_TARGET_URL back to stored inside SIP - it's necessary for 'delete'-links.