Removing LanguagePack from models/database.
Remove unnecessary management commands (distributed server).
Remove unnecessary functions and api endpoints.
Moving functions specific to language pack download to languagepackdownload.py
Updating management command params to default properly on distributed server.
Removing bogus imports from languagepackdownload
Remove central server command from distributed app.
Remove central server paths and functions from i18n app.
Remove outdated parameter is_central_server
Merge pull request #1737 from bcipolli/i18n-refactoring

I18n refactoring
Moving central-only code to the central server.
Move the app-settings importer into a module, so it can be used generically (central)
Merge pull request #1747 from bcipolli/khanload-refactor

Moving central-only code to the central server repository.
Removing internationalized exercises from the repo.  Boo.
Removing deleted testing decorator from coachreports.
Removing deleted testing decorator from distributed.
Removing deleted testing decorator from facility.
Removing deleted testing decorator from main.
Removing deleted testing decorator from updates.
Fixing testing settings to remove unnecessary global dependency.