Layer manager - control initial layer ordering

[perrygeo]

The default behavior for the layer manager is to float each newly activated layer to the top of the "Active" list. This may not always be the desired behavior

Minimum requirements

Have a boolean flag "base_layer" which would force that layer to be added to the end/bottom of the layer list

Ideally

Have an float field "layer_order" that would determine what index to insert itself into the layer list.

• 0.0 would mean always go to the bottom (still "above" the actual OL base layer though)
• 100.0 would mean always go to the top.
• Any number 0 < x <100 would be scaled from 1 to n-2 (layer 0 and layer n-1 are reserved) and the layer would be be inserted at that index.