Pubkey converter refactor

[schimih]

• Pending the PubkeyConverter refactoring and sovereign chains, the actual hrp erd should not be a constant and unchangeable value.
• Changes:

1. Address(..) accepts now an optional hrp, other than the default one DEFAULT_HRP= "erd";
2. _decode_bech32(..) doesn't check for "erd" anymore and returns the decoded hrp;
3. Install libtinfo5 for ubuntu-latest.