Internationalize TraitsUI

It would be nice to be able to have fully internationalized applications using TraitsUI. While doing this properly would require the developers writing the applications to follow best practices, there are some things which can be done to help within TraitsUI.

- use gettext/ngettext for hard-coded user-facing text (eg. dialog button labels, default window titles, etc.)
- use localized formatters for dates, times and numbers, particularly for read-only text.
- if the toolkit doesn't do it for us, use appropriate evaluators to convert text to datetime and numeric values.
- bundle translation files with TraitsUI where they can be used.