Implement drawing layers

[rbarker-dev]

• Allow layers to be generated built up
• Provide alpha slider on drawing layers
• Enable a layer preview in the menu that adds a tile for each layer
• Add Show all layers toggle
• Add Hide other layers (accept for active)
• Add layer naming
• Add duplicate layer
• Add remove layer
• Add add layer

1. All layers shall be added on top of the previous layer
2. Each drawing layer is based on a default drawing canvas (transparent canvas)
   a. exception is if the duplicate layer setting has been set
3. The default layer is always called Base Layer
4. Base Layer cannot be deleted
5. The other drawing layers will be z-indexed above Base Layer
6. When a drawing layer is deleted the layer below is made the active layer
   a. if other layers are hidden then Show all layers occurs