Better protobuf codes generation
Better protobuf codes generation

Use add_custom_command() to generate protobuf codes. When protobuf
source is updated there is no need to run cmake anymore. The generated
codes are put into binary directory so that there will be no conflicts
when we are running multiple chain configurations.

btccom/btcpool,btccom/btcpool,btccom/btcpool,btccom/btcpool,btccom/btcpool,btccom/btcpool,btccom/btcpool,btccom/btcpool