LB3 model import: convert definition of nested properties

[bajtos]

The syntax used for property definitions is slightly different between LB3 and LB4. The initial implementation of the import command is converting only top-level properties. We should convert nested properties too, both in anonymous objects and arrays.

An example of a model with nested properties:

{
  "name": "Product",
  "properties": {
    "rating": {
      "average": "number",
      "totalVotes": "number",
    }
  }
}

Acceptance criteria

• Implement the feature as described above, including automated tests
• Update Importing-LB3-models.md, remove the relevant point from the list of known limitations