Fix a few bugs about io

[Hydrop002]

• When importing a bedrock model, if there are both locators with rotation and without rotation in the same group, those locators without rotation may incorrectly get rotated. e.g.

  {
  "name": "bone",
  "pivot": [0, 0, 0],
  "locators": {
      "locator": {
          "offset": [0, 0, 0],
          "rotation": [-20, -35, 60]
      },
      "locator2": [0, 0, 0]
  }
  }

• Parsing of modded_entity always encounter problems, such as bone rotation problem caused by addChild out of order. So I improved it a little bit. I haven't considered model formats for versions of 1.17+ because I haven't read the code for those versions yet.

[JannisX11]

The locator issue is a good catch 👍 Will look at the modded entity import code another time. This feature is no longer supported for more recent versions, so it is more or less deprecated.