Revise dependencies

[mcvnh]

• pbkdf2_elixir
• extended_key
• bech32
• httpoison
• jason
• websockex
• phoenix_pubsub

[mcvnh]

• Extended key is safe but it does not work with OTP 24 at this moment, created a pull requests in his repo.
• The both dependencies HTTPoison, and Websocket are used to connect to the internet, might contains unsafe code, but with the number of people who are using, and download it every day, it seems ok, but better to implement my own clients instead. Future....