Update frontend to match new data API response format

[robhudson]

In PR #462 the API response format changed. This issue will outline how to get set up locally for testing and what the new API format looks like.

To get set up locally with data, run the following commands:

• git checkout -b transpose-frontend origin/transpose-frontend, or if you've already checked it out locally, switch to that branch.
• make build, then make shell, then ./manage.py migrate to install the new tables and migrate existing data.
• ./manage.py import_desktop_aggs nightly for the "nightly" channel. Repeat for "beta" and "release" if you want the full set of data across channels.
• Exit out of the shell and launch the app like usual.

To view the data locally you can launch the the backend with make up and hit it with curl. Here's an example curl command:

curl -X POST -H "Content-Type: application/json" -d '{"query": {"aggregationLevel": "version", "channel": "beta", "os": "Windows", "process": "parent", "probe": "gc_ms"}}' localhost:8000/api/v1/data/ | python -m json.tool

Here's an example response, truncated a bit:

{
    "response": [
        {
            "version": "74",
            "os": "Windows",
            "build_id": "*",
            "process": "parent",
            "metric": "gc_ms",
            "metric_key": "",
            "metric_type": "histogram-exponential",
            "total_users": 14315648,
            "histogram": {
                "0": 75661.0819,
                "1": 365553.2612,
                ...
            },
            "percentiles": {
                "5": 3,
                "25": 40,
                "50": 57,
                "75": 81,
                "95": 160
            },
            "client_agg_type": "summed_histogram",
            "total_addressable_market": 2874783
        },
       {
            "version": "75",
            "os": "Windows",
            "build_id": "*",
            "process": "parent",
            "metric": "gc_ms",
            "metric_key": "",
            "metric_type": "histogram-exponential",
            "total_users": 12303058,
            "histogram": {
                "0": 47542.252,
                "1": 269477.5914,
                ...
            },
            "percentiles": {
                "5": 6,
                "25": 40,
                "50": 57,
                "75": 81,
                "95": 190
            },
            "client_agg_type": "summed_histogram",
            "total_addressable_market": 2631611
        },
        ...
    ]
}