Add stronger algorithms for message authentication and key exchange.

SHA-2 from JCE was used to add support for
- message authentication
  - hmac-sha2-256
  - hmac-sha2-512
- key exchange as described in https://tools.ietf.org/html/rfc3526
  - diffie-hellman-group14-sha256
  - diffie-hellman-group16-sha512
  - diffie-hellman-group18-sha512

Use blocking queue for packets.

[maven-release-plugin] copy for tag ganymed-ssh2-262

[maven-release-plugin] copy for tag ganymed-ssh2-261