app.listen now after creation of event
Merge pull request #11 from songster-project/backend/fixingModelsBeforeAppListen

app.listen now after creation of event
added express validator (same as LF)
post route for playlists
added _id to passport.js users because i need them later on
implemented get requests
put of a song
created delete method
autoformat
changed status codes
also fixed that i cannot make update on ressources i do not own
added check that the owner_id of the song must be set and it must be set to the user wanting to post the ressource