Date field ordering should vary by region, not just by language

[1ec5]

OpenHistoricalMap/iD#185 added input fields to the Start Date and End Date fields are are arranged according to the user’s language, but not according to the user’s full locale. If the user sets a locale of en-GB, iD only considers the en part of the locale code. As a result, English speakers always see the fields in month–day–year order, regardless of dialect, because the en locale means American English.

Originally reported on the forum.