Donations controller

[vincemtnz]

Adds an endpoint to fetch the sum of all donations within a date range. For example:

GET /api/donations/totals?start=2018-12-01&end=2018-12-31
{
    "data": {
        "total_donations": {
            "AUD": "207.93",
            "CAD": "205.79",
            "CHF": "152.81",
            "EUR": "129.86",
            "GBP": "113.89",
            "NZD": "221.08",
            "USD": "159.81"
        }
    },
    "meta": {
        "end": "2018-12-31",
        "start": "2018-12-01"
    }
}

Leaving out the start and end query parameters will default to donations in the current calendar month.

If you only specify a start date, it will search from start to the end of the current calendar month. E.g.

GET /api/donations/totals?start=2018-10-01
{
    "data": {
        "total_donations": {
            "AUD": "909.91",
            "CAD": "900.53",
            "CHF": "668.68",
            "EUR": "568.27",
            "GBP": "498.33",
            "NZD": "967.44",
            "USD": "699.32"
        }
    },
    "meta": {
        "end": "2018-12-31",
        "start": "2018-10-01"
    }
}

If you provide a start date that is greater than the end date, the endpoint responds with an 400 Bad Request (the error raised is ArgumentError, 'Invalid date range').