Update tile grid option  descriptions
Update tile grid option  descriptions

In version 6 coordinate increase downwards.  Add a description for "sizes"
openlayers/openlayers,ahocevar/openlayers,stweil/ol3,geekdenz/ol3,ahocevar/ol3,adube/ol3,bjornharrtell/ol3,geekdenz/openlayers,stweil/openlayers,oterral/ol3,geekdenz/ol3,oterral/ol3,oterral/ol3,openlayers/openlayers,openlayers/openlayers,stweil/openlayers,stweil/ol3,ahocevar/openlayers,geekdenz/ol3,stweil/ol3,ahocevar/ol3,stweil/ol3,stweil/openlayers,geekdenz/openlayers,adube/ol3,bjornharrtell/ol3,ahocevar/ol3,ahocevar/openlayers,bjornharrtell/ol3,geekdenz/openlayers,adube/ol3,geekdenz/ol3,ahocevar/ol3