Ensure that the best available IP is always used for all supported
safe-search providers. This is accomplished by periodically checking
DNS for the most recent list of IP addresses associated with each
provider.

Signed-off-by: Gregory L. Dietsche <gregory.dietsche@cuw.edu>

If safe search is built directly into an image, the /etc/config/dhcp
file will have multiple entries added to it after using sysupgrade
for the nth time (2 or more sysupgrade cycles).

In /etc/config/dhcp, this bug creates duplicate entries like this:

config dnsmasq
	list addnhosts '/etc/safe-search/enabled'
	list addnhosts '/etc/safe-search/enabled'

This patch ensures that safe search only registers itself one time.

Signed-off-by: Gregory L. Dietsche <gregory.dietsche@cuw.edu>

This package forces the use of Google and Bing safe search by default.
It does this by adding hosts files for dnsmasq to use. These hosts replace the
normal IP addresses for Google and Bing with addresses that force safe
search to be turned on all the time.

Google and Bing Safe Search are suitable for most businesses, schools, and
families who wish to block adult content. This package also offers
YouTube's restricted and 'restricted moderate' via a configuration
option. The reason that this is not enabled is that it is probably more
suitable for children rather than a wide audience.

This package is designed so that other services that offer safe search can be
added easily in the future.

For more information about safe search please visit these URLs:
- https://support.google.com/websearch/answer/186669
- https://help.bing.microsoft.com/#apex/18/en-US/10003/0
- https://support.google.com/a/answer/6212415

Signed-off-by: Gregory L. Dietsche <gregory.dietsche@cuw.edu>