Support EPSG:4326

[bhousel]

It's not obvious how, but this would allow us to support a lot more WMS servers.

The issue is be that we'd be getting back an image that is either not square, or that is square but would need to be scaled vertically.

e.g.

Alaska in EPSG:3857: (0/4/4) http://basemap.nationalmap.gov/arcgis/rest/services/USGSImageryOnly/MapServer/export?bbox=-20037508.342789244%2C7514065.628545966%2C-17532819.79994059%2C10018754.17139462&bboxSR=3857&layers=&layerDefs=&size=&imageSR=&format=png&transparent=false&dpi=&time=&layerTimeOptions=&dynamicLayers=&gdbVersion=&mapScale=&f=html

Alaska in EPSG:4326 http://basemap.nationalmap.gov/arcgis/rest/services/USGSImageryOnly/MapServer/export?bbox=-180%2C55.7765730186677%2C-157.5%2C66.51326044311188&bboxSR=4326&layers=&layerDefs=&size=&imageSR=4326&format=png&transparent=false&dpi=&time=&layerTimeOptions=&dynamicLayers=&gdbVersion=&mapScale=&f=html

from http://www.maptiler.org/

== Tile Boundaries ==
WGS84 datum (longitude/latitude):
-180 55.7765730186677
-157.5 66.51326044311188

Spherical Mercator (meters):
-20037508.342789244 7514065.628545966
-17532819.79994059 10018754.17139462

Pixels at zoom 4:
0 1024 256 1280