Enhance Fusion to support multiple baselayers

[liuar]

It has been lasting years that MapGuide/Fusion users would like to have a Fusion viewer that supports multiple baselayers displaying in a single map, like the ajax viewer.

Currently, Fusion just display the first baselayer group and ignore any other groups regardless they are baselayer groups or normal groups, which makes lots of issues when using combined baselayers and normal layers in a map.

Since Openlayers restricts that a map can contain only one baselayer, I make a workaround to enable multiple baselayers which treat all the baselayers as nomal layers. Please see the attached patch for details.

--Arthur