Clue object structure

[alexis-martel]

Change the structure of the clues object from this:

"clues": {
    "across": {
      "1": "Example clue 1-Across"
    }
  }

to something like this:

"clues": {
    "across": {
      "1": {
        "content": "Example clue 1-Across",
        "hint": "This is the hint to 1-Across",
        "links": ["1-Down", "2-Across"],
        "media": [
          {
          "type": "image",
          "source": "example.com/image.png"
          }
        ]
      }
    }
  }

to allow fixing issues #77 and #60.