suggest to simplify log messages output when node starts syncing and in IBD mode

[chanhsu001]

when syncing node is in IBD(Initial Block Download) mode, the program prints every block information, with block height increasing.
it's not necessary to log every block, instead print first block, the last block within each epoch, and also print this epoch statistic information, including:

• the number of blocks
• the total number of transactions
• the total number of cycles(if possible)
• the total block size
• the time spent

from Ian's suggestion