Performance tune-up

[dorjesinpo]

1. Increase Event (batch) size. Keep PUT soft limit
2. Use bsls::BlockGrowth::BSLS_CONSTANT (instead of geometric) for pools
3. Avoid mwcu::MemOutStream while validating in Cluster
4. StorageManager::processReceiptEvent in IO thread (minus one thread switch)
5. FileStore generates Receipt at the end of received batch processing
6. Change FileStore storage builder size adjustemnt logic
7. Refactor dispatcherFlush

[hallfox]

lgtm, what performance stats does this affect?

[dorjesinpo]

lgtm, what performance stats does this affect?

This affects latencies in the (capmon) tests with multiple queues in the same cluster (cluster thread is a bottleneck)