`String` -> `Arc<str>`

[hinto-janai]

What

The Collection has many cloned String's, and slightly different versions of those String's are often created, like in Search where .to_lowercase_ascii() is applied each search.

This is inefficient.

Todo

1. All String's, notably Artist::name, Album::title, Song::title should be Arc<str> so they can be cheaply cloned
2. Lowercase (maybe uppercase too) versions should be pre-calculated and stored in the Collection