Move caching to src/cache/; Finalize API parsing fixes

Font and user cache code has been moved to special files, independant from src/config.rs

API parsing changes have been properly tested, and last.fm API JSON is now trace-logged for debugging convenience.

Add custom font support.

lots of stuff. theming basically done, added some logging, frontend basically done.

config done

fix packages, implement caching

API deserialization structs