foreground blocks, blocks on different layers

[batram]

1. Should all layers that exist in UCH be selectable and not just limit it to one selected layer for background and foreground?
2. How should the layer data be stored?
   • more magic numbers in blockID
   • add a new attribute in XML for layers
3. What is the nicest way to integrate the selection into the block placement process?
   • Just hit a button and cycle through all
   • Dropdown Selection GUI (might be a lot of work)
   • Best way to show information about the layer when building

[batram]

6c960cf lays the ground work for this feature, still some polishing and functionality to implement.

For example:

• A hotkey to only show or highlight the blocks on the currently selected layer
• permanently show the selected layer in place phase