Added support for multiple IP's per interface

[digimer]

• Created Database->get_mac_to_ip()
• Updated Database->insert_or_update_mac_to_ip() to find an entry using both the IP and MAC address.
• Updated Network->get_ips() to store only the first IP it finds on an interface as the main IP (for use in /etc/hosts, etc) and to store it and any other IPs in a new hash.
• Updated scan-network to use the new hash above to record them in the 'mac_to_ip' table. Similarly, before marking an IP as removed, it checks to see if it's an alternate IP.