Implement loading of cube data from JSON file

assets/robocraft/asset_notes.md

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+# Asset Retrieval
+
+[UABE](https://github.com/SeriousCache/UABE) is pretty great for this.
+
+## Cubes
+
+Cube data is contained in `cubetypelist_steam` as a sub-asset (UABE dumps the actual asset as `unnamed asset-CAB_e94be3f69d8179602fb05811b2ba5579-4300557138948789011`).
+
+I've written a Python script to process that asset (exported as JSON) into the JSON format I've designed.