Scalatest integration

We need special matcher for json strings that doesn't care about object fields order. Something like that:
```scala
"""{"a": 1, "b": [1, 2, 3], "c": true }""" should equalJson(obj(
  "a" -> 1,
  "c" -> true,
  "b" -> arr(1, 2, 3)
))
``` 