Host history

Grabs data from last_seen in hosts table. Looks like that is updated from dhcpd-log-extract and rtr-log-extract in net/scripts/maintain. I am not sure if we are gonna have to do any rewriting of that in the future. As mentioned in https://github.com/OSU-Net/cyder/issues/77. Running tests right now. Was getting errors at first because you have to drop the test database. Looking good now though.