72 implements download blockchain

[capt4ce]

Description

Implementing download blockchain mechanism.

Breakdown

• Implement download blockchain
• Add additional several p2p communication service to assist blockchain download mechanism
• Add GetBlockByID and GetBlocksFromHeight in the core block service
• Add tests the things listed above
• Implement observer

Reference Issue

Close #72

Step to Test (optional)

• Deletes all the database you have
• Start first one node by running go run main.go. This command will use the config from resources/config.toml and let it run until it stacks up several blocks
• Start the second node with go run main.go --config-postfix 2. This command will run a node with config file resource/config2.toml
• Monitor the blocks both the nodes have by running go run main.go --ip 127.0.0.1:8001 and go run main.go --ip 127.0.0.1:8002 in api/client/GetHostInfo in separate terminal
• checks periodically until this second node successfully download the blocks from the first node

Notes:

• To check the blocks that a node has is by running go run ./api/client/GetHostInfo.client --ip 127.0.0.1:3001 (please adjust the ip part). And theres's a section ChainStatus in the returned data