Add an extent restriction on the mapbox layer example
Add an extent restriction on the mapbox layer example

This fixes a bug where the OL map would allow much larger resolution than
mapbox.

ahocevar/ol3,tschaub/ol3,ahocevar/openlayers,geekdenz/openlayers,ahocevar/ol3,ahocevar/ol3,geekdenz/ol3,oterral/ol3,openlayers/openlayers,geekdenz/ol3,stweil/openlayers,bjornharrtell/ol3,adube/ol3,tschaub/ol3,ahocevar/openlayers,adube/ol3,geekdenz/openlayers,openlayers/openlayers,ahocevar/ol3,tschaub/ol3,stweil/ol3,stweil/openlayers,openlayers/openlayers,geekdenz/ol3,stweil/openlayers,adube/ol3,stweil/ol3,stweil/ol3,oterral/ol3,oterral/ol3,geekdenz/ol3,stweil/ol3,bjornharrtell/ol3,tschaub/ol3,bjornharrtell/ol3,ahocevar/openlayers,geekdenz/openlayers