Setup dnsmasq and .vspi domain

Replaces udhcpd with dnsmasq, which is also responsible for resolving DNS requests to wireless clients, allowing the vspi to host websites and other services on the `.vspi` fake TLD within the wireless network.

Wordpress is set up on the `vspi` host, which is resolved by `vspi` or the fully-qualified `vspi.vspi`. Additional web services can be served through nginx by adding new virtual servers and adding the new hostnames
to `/etc/hosts` e.g. `wiki.vspi` could be resolved with

    10.0.10.1 wiki

Also, enables ip forwarding so the raspi can route internet requests to an upstream router. If this is undesirable for security or other reasons, the `sysctl` line can be removed.