Developer can send in arrays of values

[ajturner]

var dataset = {
  "values": [
     {"height": 52},
     {"height": 103},
     {"height": 38}
   ]
}

[dbouwman]

Notes:

• refactor Cedar so we always pass data array to vega
• prior to the passing the array to vega, validate that the first object has the required properties specified in the mappings
• add error handlers to account for AGS sending 200's-that-are-500's and other oddities