Merge maps script

`merge-maps`, should merge maps that scanner produces.

We'll receive following input:

```json
{
  "/path/to/filename/foo.js":  {
    "context": "fooContext",
    "messages": {
      "Normal message": [{ "point": 17, "column": 17, "line": 2 },
        { "point": 37, "column": 17, "line": 4 }],
      "n\0One Apple\0Many apples":  [{ "point": 17, "column": 17, "line": 2 }]
    }
  },
  "/path/to/filename/bar.js":  {
    "context": "default",
    "messages": {
      "Normal message": [{ "point": 17, "column": 17, "line": 2 },
        { "point": 37, "column": 17, "line": 4 }],
      "n\0One Apple\0Many apples":  [{ "point": 17, "column": 17, "line": 2 }]
    }
  }
}
```

On base of it ,we should resolve following map

```json
{
  "Normal message":  {
    "fooContext":  [
      { "fileName": "/path/to/filename/foo.js", "point": 17, "column": 17, "line": 2 },
      { "filename": "/path/to/filename/foo.js", "point": 37, "column": 17, "line": 4 }
    ],
    "default":  [
      { "fileName": "/path/to/filename/bar.js", "point": 17, "column": 17, "line": 2 }
    ]
  }
  "n\0One Apple\0Many apples":  {
    "fooContext":  [
      { "fileName": "/path/to/filename/foo.js", "point": 17, "column": 17, "line": 2 },
      { "filename": "/path/to/filename/foo.js", "point": 37, "column": 17, "line": 4 }
    ],
    "default":  [
      { "fileName": "/path/to/filename/bar.js", "point": 17, "column": 17, "line": 2 }
    ]
  }
}
```