Add no-fallback mode for localizations

[tjcouch-sil]

User Story
As a UI translator, I want to be able to see which localized strings are not localized in my target locale so that I can effectively target obvious, highly-impactful strings.

Description
Add a way to disable using fallbacks for localized strings. Maybe this can just be a setting or something. Essentially, we need to add some way to make only localized strings that are available in the current interface locale to be shown and for all untranslated strings to show up as localized string keys