Use MeshStamper to lower terrain outside boundary

[Besjan]

• [x] Create TerrainStamper with height 0 and terrain from terrain tile
• [x] Create FreeCurve node with curve points as boundary points: http://community.archimatix.com/runtime-scripting/controlling-freecurve-through-code/
• [x] Create Square node with size and position as terrain tile
• [x] Use ShapeMerger with difference
• [x] Fix terrain stamper heights

• [x] Fix terrain gaps (will be fixed when creating lower res terrains)

• [x] Foreach boundary terrain, lower outer vertices

[Besjan]

Using Archimatix