feat(passkit): Work towards localizable pass files

[ueman]

This works towards localizable passes. In particular, it adds naive parsing of the strings files.

• no external API to read the various entries in a localized way
• no localized images
• it still uses UTF-8 instead of UTF-16
• parsing is done via regex, which might fail

Related to https://github.com/ueman/passkit/issues/8