Fix bug parsing raw Fitbit calories JSON data

[jenniferfedor]

Every minute-level record in the raw Fitbit activities-calories-intraday dataset is expected to contain level, mets, time, and value elements. However, we've found that it's possible for raw intraday calories time series data to contain only time and value elements. For example:

"activities-calories-intraday": {
    "dataset": [
      {
        "time": "00:00:00",
        "value": 1.39192
      },
      {
        "time": "00:01:00",
        "value": 1.5311120000000003
      },
    ]
}

Currently, parsing raw Fitbit intraday calories JSON data fails with these data specifically, as well as more broadly if level, mets, and/or value elements are not present in at least one minute-level record for a participant. To fix this, before parsing each minute-level record into a row of data, we first check if the record contains all expected elements instead of assuming they are present. If one or more expected elements are missing, that minute-level record is discarded. If all minute-level records within an intraday dataset are missing one or more expected elements, this has the effect of discarding the entire day of data. Downstream, Fitbit intraday calories features are computed only from "complete" minutes of data.