Set PublicPrivate KeyPair with values from DHT, use salt from DHT

[rmatil]

The public private key pair should not be transferred manually from one client to another. Therefore, we save the publicKey, privateKey (encrypted with the password & salt from the user) and the salt in the DHT.

Add the following:

• Join network without any key pair (Client#initPeerDht)
• Fetch public key, private key and salt from the DHT
• Generate secret key for the user using the pw and the salt
• Add secret key to the user
• Decrypt the private key using the secret key from the user
• Set public private key pair in PeerDHT

Blocker: tomp2p/TomP2P#123