Add timestamp querystring to mbtiles preview. Fixes #760.
Add timestamp querystring to mbtiles preview. Fixes #760.

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