OBMFULL-6103 Add a new configuration key, transaction-tolerance-timeout
OBMFULL-6103 Subtract lastSync by conf.transaction-tolerance-timeout-seconds 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.
This configuration key has been created to lower synchronization bugs
which could occur with synchronization races condition.
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