EXT-8310 FIXED Incorrect currency format in the Buy L$ floater.

Changes in the Buy L$ floater:
* Set system locale before formatting currency.
* Made money format configurable (via strings.xml).
* Placed the "L$" label to the right of the line editor in FR locale.

Details:
Actually, the proper way to fix this and similar number formatting bugs would be to set the system locale at startup, but:
1. That triggers assertions when parsing locale-agnostic XML files like avatar_skeleton.xml.
2. I'm wary of making such global changes so close to the 2.1 release.
Therefore I just temporarily override current locale before formatting a number and restore the previous locale afterwards.

Reviewed by Tofu at https://codereview.productengine.com/secondlife/r/751/

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branch : product-engine