Remove system getifaddrs dependency

utils.rb - remove system-getifaddrs import
quaff.gemspec - removed system-getifaddrs dependency
call.rb - modified call to utils.local_ip to get ip_address
endpoint.rb: - modified call to utils.local_ip to get ip_address, added local_hostname to initialization in BaseEndpoint class

Two minor glitches detected:
- additional changes are required when local_hostname is supplied
- on Windows 7 machine INVITE is sent twice, whereas on Ubuntu 14.04.1 LTS number of messages is correct

I will take a look at these issues later, currently I have more urgent issues to deal with. Feel free to reject if having these issues is not ok for you.