Added basic blacklisting

[Akilan1999]

Basic blacklisting

Implementation to blacklist nodes based on their Peer ID (i.e Public key).

Storage for blacklisting nodes: Pogreb

Current blacklisting done:

• Ensuring nodes in the blacklist is not in the peerlist

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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