website: create habtm join table between genres and artists
website: allow associations to be order by listens and popularity
website: hide loading indicator when displaying error
website: create helper for creating top lists of models
website: display top lists of songs, genres and albums when listing artists
website: create helper for listing hyperlinked models in a sentence
website: override to_s on models and display :display
website: show only top 3 of songs, artists, etc. in search results
website: refactor concerns and add find_or_create_by_hash to concerns

Make Base a proper concern.

Add find_or_create_by_hash to Base concern, and allow other concerns
to extend it.

Use Genre to test find_or_create_by_hash from its concerns.