Switch to a JSON-based configuration and update the dependencies

Dependencies versions:
  - Athena-Core 1.3.0
  - Athena-Entities 1.2.2
  - Athena-Graphics 1.2.0
  - Athena-Physics 1.1.2
  - Bullet 2.81
  - FreeType 2.4.9
  - rapidjson 0.11.0