Made it possible to have just a subset of layer preview parameters
Made it possible to have just a subset of layer preview parameters

mapzen/TileStache,mpuig/TileStache,SEL-Columbia/TileStache,mpuig/TileStache,TileStache/TileStache,Billups/TileStache,SEL-Columbia/TileStache,Blechhirn/TileStache,TileStache/TileStache,moskvax/TileStache,Blechhirn/TileStache,jbants/TileStache,Blechhirn/TileStache,robpvn/Vector-Tile-Research,Kosta-Github/TileStache,jbants/TileStache,TileStache/TileStache,Kosta-Github/TileStache,mojodna/TileStache,mojodna/TileStache,MetGIS/TileStache,moskvax/TileStache,Billups/TileStache,Billups/TileStache,mapzen/TileStache,mapzen/TileStache,robpvn/Vector-Tile-Research,SEL-Columbia/TileStache,jbants/TileStache,moskvax/TileStache,robpvn/Vector-Tile-Research,MetGIS/TileStache,Kosta-Github/TileStache,MetGIS/TileStache