Adding nearby and recommended parks to park JSON payload

Addresses #53. Also includes some minor code and project cleanup.

Sample JSON output from `/parks/search/?slug=boston-common-110`:

```
{
  "110": {
    "access": "Yes",
    "name": "Boston Common",
    "address": "148 Tremont Street, Boston",
    "url": "/parks/boston-common-110/",
    "change_url": null,
    "owner": "City of Boston",
    "description": "The oldest park in the United States, the Common has been shared land since 1634 and holds a unique place in the history of Boston and the nation. Though the landscape has changed from pastures and militia training grounds to a well-loved park with open lawns, shaded pathways, ballfields, tennis courts and a playground, the Common remains an active meeting ground in the heart of historic Boston. For over 350 years it has been a center and a mirror of civic life.rnrnToday, Boston Common is the anchor for the Emerald Necklace, a system designed by Fredrick Law Olmsted, parks that connect many of Boston's neighborhoods.",
    "images": [
      {
        "src": "/media/cache/6a/9e/6a9ee81a2ce40e4ae08ea86facf30853.jpg",
        "large_src": "/media/cache/bd/3f/bd3f02479881f6f6dbe61ee304b8e079.jpg",
        "caption": "Photo by jennikonrad"
      },
      {
        "src": "/media/cache/2c/9a/2c9ac66e62e15c3e16badc4bfbaf221b.jpg",
        "large_src": "/media/cache/d6/ae/d6aebae6123acb85b180183b9b21d607.jpg",
        "caption": "Photo by treycliff"
      },
      {
        "src": "/media/cache/65/ec/65ecdf3ceb0b7fd675e93752beb955d1.jpg",
        "large_src": "/media/cache/87/0e/870ed50379be737458fecf634aacf337.jpg",
        "caption": "Photo by wili_hybrid"
      },
      {
        "src": "/media/cache/87/32/873299ad5ad2da38e421f2782123e6fb.jpg",
        "large_src": "/media/cache/3c/78/3c78c19164574c7557bcec093a4070c1.jpg",
        "caption": ""
      },
      {
        "src": "/media/cache/28/96/28964f8f202775315df3e8cf68012469.jpg",
        "large_src": "/media/cache/19/a6/19a6c310e985216400f432ad9f951111.jpg",
        "caption": ""
      }
    ],
    "recommended_parks": [
      {
        "image": {
          "src": "/media/cache/9e/ff/9efff9d495ae275e6b7faa896bc43e55.jpg",
          "large_src": "/media/cache/54/99/54994daf69279eb161d3218f50d3eaf7.jpg",
          "caption": ""
        },
        "id": 562,
        "name": "The Esplanade"
      },
      {
        "image": {
          "src": "/media/cache/6a/9e/6a9ee81a2ce40e4ae08ea86facf30853.jpg",
          "large_src": "/media/cache/bd/3f/bd3f02479881f6f6dbe61ee304b8e079.jpg",
          "caption": "Photo by jennikonrad"
        },
        "id": 110,
        "name": "Boston Common"
      }
    ],
    "nearby_parks": [
      {
        "image": {
          "src": "/media/cache/9e/ff/9efff9d495ae275e6b7faa896bc43e55.jpg",
          "large_src": "/media/cache/54/99/54994daf69279eb161d3218f50d3eaf7.jpg",
          "caption": ""
        },
        "id": 562,
        "name": "The Esplanade"
      },
      {
        "image": {
          "src": "/media/cache/6a/9e/6a9ee81a2ce40e4ae08ea86facf30853.jpg",
          "large_src": "/media/cache/bd/3f/bd3f02479881f6f6dbe61ee304b8e079.jpg",
          "caption": "Photo by jennikonrad"
        },
        "id": 110,
        "name": "Boston Common"
      }
    ]
  }
}
```