Add authorization mechanism

Flow:
1. @deviceland receives ΨAUTH command
2. @deviceland sends ΨAWAITING_CODE DM to @FunWithDevices
3. @deviceland generates auth code
4. @FunWithDevices sends ΨAUTH_CODE:<auth-code> DM to @deviceland
5. If sent auth code matches the generated one
    then send ΨACCESS_GRANTED DM to @FunWithDevices
    else send ΨACCESS_DENIED DM to @FunWithDevices
Once authorized, the Bakha.Commands.Authorized set of commands are
available to be invoked.