Exposed new options in FdbDatabaseOption and FdbTransactionOption

- db.SetMaxWatches(..), SetMachineId(..) and SetDataCenterId(..)
- tr.WithTimeout(..), WithRetryLimit(..)
Added possibility to specify default timeout and retrylimit on the database

- All new transactions will be configured automatically
- Added Timeout/RetryLimit settable properties on FdbTransaction
- Made FdbTransaction.SetOption(...) internal
Added fdb_future_cancel native method

- Renamed FdbFuture.Abort() to FdbFuture.Cancel() to follow the C API
- Call fdb_future_cancel from the CancellationHandler (when the parent CancellationToken gets triggered)