Represent traces as array rather than dictionary

[trombonehero]

SOAAP currently names [sub]traces in the call graph using string names and puts them into the top-level SOAAP object. It might ease the complexity burden a bit if we instead put an array of traces into the top-level object and referred to each trace by index within this array instead of by name.

That is, instead of:

"vulnerability_warning": [
  {
    "function": "_ZNK6SkMask16computeImageSizeEv",
    "sandbox": "capsicum",
    /* ... */
    "trace_ref": "!trace0"
  }
],
"!trace0": {
    "name": "!trace0",
    "trace": [
      {
        "function": "_ZNK6SkDraw16drawBitmapAsMaskERK8SkBitmapRK7SkPaint",
        "location": /* ... */
      },
      {
        "trace_ref": "!trace311968"
      }
    ]
  },
}

we could have:

"vulnerability_warning": [
  {
    "function": "_ZNK6SkMask16computeImageSizeEv",
    "sandbox": "capsicum",
    /* ... */
    "trace_ref": 0
  }
],
"traces": [
  [
    {
      "function": "_ZNK6SkDraw16drawBitmapAsMaskERK8SkBitmapRK7SkPaint",
      "location": /* ... */
    },
    {
      "trace_ref": 311968
    }
  ],  
  /* ... */
]