Group nodes in three layers

[Likbjorn]

Three layers to be created:

• [x] Foreground layer for 20 nodes to interact with.
• [x] Middle layer for 20 nodes to mimic the next in-depth layer.
• [x] Background layer with non-interactable nodes which serve aesthetic purpose.

Each layer must not interact with other layers. Detailed description on content and logics of each layer to be provided in other issues.

[Likbjorn]

Nodes are logically grouped now, formally the issue is closed. Need to fill them and setup interaction though - to be described in other issues.