Translations for Rapid strings

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Rapid has always relied on using the translation strings from iD whenever we merge iD's code into ours. There are a few strings that Rapid displays differently from iD, but it hasn't been too much trouble to keep things in sync. The disadvantage is that the Rapid strings are not localizable to other languages. (see https://github.com/facebookmicrosites/Open-Mapping-At-Facebook/issues/19 )

Going forward I'd like to set up a resource on Transifex to hold just the Rapid strings, so that these can also be localized in the same way as the iD strings.