addpa command allows adding of duplicate public addresses

[Haris-Irfan]

Running addpa 4 c/BTC l/savings_wallet pa/0x71C7656EC7ab88b098defB751B7401B5f6d8976F and then running addpa 5 c/BTC l/savings_wallet pa/0x71C7656EC7ab88b098defB751B7401B5f6d8976F allows me to add the same public address to multiple contacts. I feel like a check could be put in place to ensure that duplicate public addresses are not used since two wallets cannot have the same public address!