Add placeholder abilities route callback.
Add placeholder abilities route callback.

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