Support different decimal/thousands separators

[macrigiuseppe]

There are numerous international datasets that Kepler cannot process because they use different decimal separators other than a period, such as this Buenos Aires Taxi Dataset, which uses a comma instead of a period.

In addition to commas instead of decimals, there are a few other formatting types that may be worth supporting: https://en.wikipedia.org/wiki/Decimal_separator#Examples_of_use