Support display locale and format locale being different

[hakanai]

Java 7 separated the "display locale" and "format locale" - you're supposed to use the "display locale" to fetch the strings to use, but you're supposed to use the "format locale" to fetch the formats for numbers, currencies and dates. However, the current generated API here only allows passing in 0 or 1 locales.

A wrapper object to hold all the locale-specific information is a common way to avoid the caller having to pass multiple things in every time, which could help reduce boilerplate for the caller.

(Honestly Java properties resource bundles are a mess though. It would be so much nicer if something standard were to emerge which dealt with things like plurals correctly. I know I could just create it... :( )