Layer List Improvements

Some ideas for improving the layer list usability:

1. Support ordering of the layer list that is independent from the drawing order.

This way groups of layers that belong together can be located together even though they are a long way apart in the drawing order. e.g. a set of restricted travel areas are drawn low in the order but approved travel routes across those areas are drawn high in the order. These two items should be close in the layer list so they can easily be toggled on/off together.

2. Grouped layers.

Following on from the previous point, let me define a group of layers that should be turned on/off together. E.g. If you turn on the approved routes above,  the restricted areas also turn on.

3. Mutually exclusive layers

Some layers don't make sense to shown together e.g. Freight routes that overlap (i.e. use the same road). Provide Radio buttons instead of Checkboxes in the Layer list for these types of layers.

4. Show icons/symbology in the layer list

To help the user avoid having to go to the Legend to understand the map, put the layer symbol or an icon beside every layer in the layer list. This should leverage the map service as much as possible an use the defined symbols rather than having to create icons that look like the map service symbols.

5. Layer themes

This has been mentioned as coming in a future release but I haven't seen the details. One Site may support multiple purposes e.g. a disaster response map that supports floods, cyclones, fire, oil spills, etc. Provide a layer theme capability to show a collection of layers relevant to one of the maps purposes e.g. Layers to support as Oil Spill are different to those needed for a Flood.