A new and improved device manager (woohoo). We support IPv6 now and have fixed...

A new and improved device manager (woohoo). We support IPv6 now and have fixed some bugs. Other changes have been made to prefer 'empty/zero' objects instead of null, which made using the device manger less type safe and more error prone. Unit tests for IPv6 packets will come next, so IPv6 support should be considered experimental for this commit (although in theory it should be fine if IPv4 is).