make carto reference external links open in new window to avoid getting stuck in the OS X app - closes #1593
make carto reference external links open in new window to avoid getting stuck in the OS X app - closes #1593

MappingKat/tilemill,nyimbi/tilemill,MappingKat/tilemill,mbrukman/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,tizzybec/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,Zhao-Qi/tilemill,nyimbi/tilemill,MappingKat/tilemill,fxtentacle/tilemill,tilemill-project/tilemill,florianf/tileoven,fxtentacle/tilemill,mbrukman/tilemill,mbrukman/tilemill,florianf/tileoven,tizzybec/tilemill,paulovieira/tilemill-clima,nyimbi/tilemill,fxtentacle/tilemill,MappingKat/tilemill,tizzybec/tilemill,mbrukman/tilemill,paulovieira/tilemill-clima,fxtentacle/tilemill,nyimbi/tilemill,mbrukman/tilemill,paulovieira/tilemill-clima,tilemill-project/tilemill,Zhao-Qi/tilemill,Zhao-Qi/tilemill,tilemill-project/tilemill,tizzybec/tilemill,fxtentacle/tilemill,paulovieira/tilemill-clima,MappingKat/tilemill,Zhao-Qi/tilemill,paulovieira/tilemill-clima,nyimbi/tilemill,florianf/tileoven,Zhao-Qi/tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,Teino1978-Corp/Teino1978-Corp-tilemill,tizzybec/tilemill