added blacklist commands

[Akilan1999]

Blacklist commands to blacklist nodes in the network

Required PR to be merged in Core: PeernetOfficial/core#90

Commands added to Cmd repo:

add blacklist                 Adds a node to the blacklist
list blacklist                Shows all nodes in the blacklist
remove blacklist              removes node in the blacklist

Sample output of list blacklist:

Peer ID: 026836d40a77779b7df5f1a08ca1ef8a83e15edcf0e4d8dc6ed5fc351cb60bd07c
Reason: idk
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