Add support for dynamic locale

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• use Property instead of string for translated strings
• add "supportsDynamicLocale": true to package.json and run grunt modulify
• address dynamic layout problems

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I've done the first parts of this. But I'm blocked on addressing layout issues until I can identify those issues, which requires phetsims/chipper#1319 to be addressed. So I'll come back to this.

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I tested this sim with ?stringTest=dynamic and corrected a few minor issues in the above commits. It is otherwise well-behaved. Since new development is supposed to support dynamic layout, I see no reason to keep this issue open.