Added support for private IP squids. fixes #4
Added new service to shoal to return the IP of the request. This is used
for getting an external IP of a squid if it is located in a private
network and has no public IP. This is needed for generating geo_location
data.

now using external_ip returned from the shoal service to generate
geo_data, as the external IP is the same as the public IP if the squid
has a public IP (atleast in my tests they were consistant)

Added new configuration setting to set the url of the
external_ip_service so it can be changed on the fly if the shoal
webserver changes IP.

Still needs more testing on private IP squids, but the few tests I ran
appeared to work.