Unify import style

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.

Clippy

Cleanup

Custom font support complete

Add custom font support.

Create plain theme, do some escaping, fix some busted envvars, document themes.

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

config done

API deserialization structs