allow different properties on map and layers

[tschaub]

It would be nice to separate map and layer properties. Currently, the map projection, maxResolution, minResolution, maxExtent, etc. are used as layer defaults if no similar properties are set in the layer options.

It would be nice to be able to independently set map and layer properties. So, you could have a layer in one projection and a map in another. Or you could have a layer with one minResolution and a map with a different minResolution. You can currently do this with overlays, but not when a layer is map.baseLayer.