OBMFULL-6103 Add a new configuration key, transaction-tolerance-timeout
OBMFULL-6103 Subtract lastSync by conf.transaction-timeout between CalendarBinding and EventHandler. It only concerns getSync and it's the only path before serializing the EventChanges then send it back to the client
OBMFULL-6103 Do the same thing for AddressBookBinding (lastsync - transactionTimeout)
OBMFULL-6103 Add a new hash tag of value Event.hashCode() in and Event serialization
OBMFULL-6103 add tests against BookItemsWriter
OBMFULL-6103 refactor BookItemsWriter like CalendarItemsWriter
OBMFULL-6103 add a new hash tag to the serialization of a contact
OBMFULL-6103 add the new tolerance key into obm_conf.ini.sample