relate channels to their server

this is necessary for supporting multiple irc servers in one bot config.
this also has the side effect of requiring some code in ircbot and
markov which autocreates channels to also include the server (retrieved
via the connection). this will again help keep channels coherent for
multi-server arrangements

the twitter bot change here is untested but seems like the right idea (I
haven't used the twitter package in forever)

ircbot/migrations/0017_ircchannel_server.py

@@ -0,0 +1,30 @@
+# Generated by Django 3.1.2 on 2021-04-25 16:11
+
+from django.db import migrations, models
+import django.db.models.deletion
+import ircbot.models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('ircbot', '0016_placeholder_ircserver'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='ircchannel',
+            name='server',
+            field=models.ForeignKey(default=1, on_delete=django.db.models.deletion.CASCADE, to='ircbot.ircserver'),
+            preserve_default=False,
+        ),
+        migrations.AlterField(
+            model_name='ircchannel',
+            name='name',
+            field=ircbot.models.LowerCaseCharField(max_length=200),
+        ),
+        migrations.AddConstraint(
+            model_name='ircchannel',
+            constraint=models.UniqueConstraint(fields=('name', 'server'), name='unique_server_channel'),
+        ),
+    ]