[Feature] Admin option to choose French as language

[duncan222]

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These are changes to the admin site to add French to the list of language options. It looked as if French was added as an option on all the other sites, however the French option was missing from the Admin page. I translated the "en-US" JSON file from the admin-web-angular/src/assets/i18n directory to French and placed the contents of this translation into the "fr-FR" JSON file in the same directory.

The last changes made were to the "theme-settings.cpmponent.ts" in the admin-web-angular/src/app/components/theme-settings directory, which were adding French as an option in the drop down list that is presented in the settings side bar.

Please let me know if there is anything else I can do here. Thanks