Add lockwise import script

[joeyg]

This PR adds an import script for lockwise strings. It includes a slight refactor of the firefox import script. Long term a real upgrade of this should be done. To run:

1. Checkout this branch of ios-l10n-scripts repo to be a sibling of lockbox-ios repo
2. cd lockbox-ios
3. ../ios-l10n-scripts/import-locales-lockwise.sh
4. Verify that new language files are created for the main app, credential provider extension, storyboards, and xibs. Note that if only there is no translation a new file won't be created.

[devinreams]

First attempt to import strings is over here:
mozilla-lockwise/lockwise-ios#997

[devinreams]

@kaylagalway this branch is needed for import