Tests refactor

[miporto]

• Modularize tests
• Add real artists and albums for tests

[aibarbetta]

For each entity * (for example; user, track, album, artist, ...) we should split the tests in modules:

• *.admin.spec.js creation, update, deletion, fetch
• *.me.spec.js endpoints that require the user id in the auth token
• *.extra.spec.js everything else¿?

Each one with its own constants:

• *.admin.constants.json
• *.me.constants.json
• *.extra.constants.json

[miporto]

And move them to it's own folders (test/routes/artists/..., test/routes/albums/..., etc)