Port networkTools.cpp to Mac OS X.

On Mac OS X the ioctl(SIOCGIFCONF) call will return all IPv4, IPv6
and MAC addresses, so we have to filter only the ones that have
sa_family equal to AF_INET.

I also added the common interface names for Mac OS X (en0 and en1),
to the getBestPublicIp() function. I refactored a bit the code so
that addition and reordering are easier.

Bugs: https://sourceforge.net/p/kiwix/bugs/658/
updated CHANGELOG (IP address osx)