Placement of additional nodes in 2D plane to "collapse" a single layer

[olwijn]

Second step towards supporting layerying in FlowNet:

1. Implement the placement of additional nodes in 2D based on (X,Y) or (i,j) locations of all well nodes.
2. Translate all nodes to all layers and assign depths to all newly created additional nodes. Use the mid-value of the depth interval for each layer based on the 'map' created in issue #239