LMS: adding language selector to user dashboard (WIP)
wiring for language selector
Added dark lang database fixture to bok choy tests
Acceptance test for language selector

Tests language selection feature for student dashboard
LMS: simplifying language settings modal controls UI
Moved UserPreferences to common
Added middleware for handling language changes
Added acceptance test for language persistence

Will pass once the language persistence stuff gets merged in
Store user preferences for languages

Also, refactor tests such that we're not deleting users or prefs
LMS: revising modal UI to support translators
If we run into issues with languages, use default
Add back in the fake2 language
Clean up the display and dialog to use user preferences
instead of the current language.
LMS: adding iconography to language pref on dashboard UI
LMS: adding in supplemental 'volunteer to be a translator' action to language modal
LMS: revising color of language icon
Clean up tests.
Use a given default for getting a preference
Change setlang url
Better dashboard display behavior

* Don't show sidebar if only one language is present
* only add in the default language code if it's not already present