Implement space as default thousands separator

[joewdavies]

The publications team for the DRYB used a space as a thousands separator. maybe we should implement this as the default?

[joewdavies]

could be achieved by setting the following d3 locale:

    d3.formatDefaultLocale({  
        "decimal": ",",
        "thousands": " ",
        "grouping": [3],
        "currency": ["", "€"]
    })

then using d3.format(",.2r") to format the strings