use rvido for splicing audio
song#create_preview: cut 20sec recording preview after upload (should be extracted, maybe a cool gem?)
song#add_to_cache: save preview link
add delayed job
schema
songs#index: add basic audio player for previews
generate dj, migrate
song#create_preview: make delayed because otherwise recording isnt saved in time to cut preview
song#update_cache: update cache after update, add songid to cache hash