imported openchange_user_cleanup script from old version

This is for ldb backends
user_cleanup_script updated for mysql backends
openchange_user_cleanup: pretty format and --ignore=sogo|openchange|imap option
openchange_user_cleanup: typo in help
openchange_user_cleanup: change regexp format to get connection strings
openchange_user_cleanup: ignore default to empty list
openchange_user_cleanup: enable autocommit
openchange_user_cleanup: drop sogo table instead of truncate data
Merge pull request #127 from openchange/jgarcia/user-cleanup-script

user cleanup script