Change artists field in Track

artists is now a ManyToManyField in Track, which is cleaner than
using a unique_together clause in the Meta class.

spotifyvis/migrations/0001_initial.py

@@ -1,4 +1,4 @@
-# Generated by Django 2.0.5 on 2018-06-03 23:01
+# Generated by Django 2.0.5 on 2018-06-05 20:53
 
 from django.db import migrations, models
 import django.db.models.deletion
@@ -43,7 +43,7 @@ class Migration(migrations.Migration):
             name='User',
             fields=[
                 ('user_id', models.CharField(max_length=30, primary_key=True, serialize=False)),
-                ('username', models.CharField(max_length=30)),
+                ('user_name', models.CharField(blank=True, max_length=30)),
             ],
             options={
                 'verbose_name': 'User',
@@ -71,15 +71,11 @@ class Migration(migrations.Migration):
         migrations.AddField(
             model_name='track',
             name='artist',
-            field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE, to='spotifyvis.Artist'),
+            field=models.ManyToManyField(to='spotifyvis.Artist'),
         ),
         migrations.AddField(
             model_name='track',
             name='users',
             field=models.ManyToManyField(to='spotifyvis.User'),
         ),
-        migrations.AlterUniqueTogether(
-            name='track',
-            unique_together={('track_id', 'artist')},
-        ),
     ]

spotifyvis/migrations/0002_auto_20180605_2347.py

@@ -1,4 +1,4 @@
-# Generated by Django 2.0.5 on 2018-06-05 02:09
+# Generated by Django 2.0.5 on 2018-06-05 23:47
 
 from django.db import migrations
 
@@ -11,8 +11,8 @@ class Migration(migrations.Migration):
 
     operations = [
         migrations.RenameField(
-            model_name='user',
-            old_name='username',
-            new_name='user_name',
+            model_name='track',
+            old_name='artist',
+            new_name='artists',
         ),
     ]

spotifyvis/migrations/0003_auto_20180605_0211.py

@@ -1,18 +0,0 @@
-# Generated by Django 2.0.5 on 2018-06-05 02:11
-
-from django.db import migrations, models
-
-
-class Migration(migrations.Migration):
-
-    dependencies = [
-        ('spotifyvis', '0002_auto_20180605_0209'),
-    ]
-
-    operations = [
-        migrations.AlterField(
-            model_name='user',
-            name='user_name',
-            field=models.CharField(blank=True, max_length=30),
-        ),
-    ]