leaflet layer order - layer deactivated

[Ben Wyss]

In the HRDE application one can change the layer order. But there is a issue:

1) add layer "A"
2) add layer "B"

Move layer B on top, deactivate it and keep only layer "A", click on the map: you'll get data from layer "B" which is at the top, but is off and hidden

We will need to identify when a layer is activated and or deactivated, the we need to add some logic that will manage the Utfgrids accordingly.