Fix: increase LocalSettings.key max_length to 50

LND-ReconnectInterval (21 chars) exceeds the previous max_length=20
on LocalSettings.key. SQLite ignores the constraint, but PostgreSQL
enforces VARCHAR(20) strictly and raises DataError when saving it.

Fixes #460

gui/migrations/0040_alter_localsettings_key.py

@@ -0,0 +1,16 @@
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('gui', '0039_inboundfeelog'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='localsettings',
+            name='key',
+            field=models.CharField(default=None, max_length=50, primary_key=True, serialize=False),
+        ),
+    ]

gui/models.py

@@ -187,7 +187,7 @@ class Rebalancer(models.Model):
         app_label = 'gui'
 
 class LocalSettings(models.Model):
-    key = models.CharField(primary_key=True, default=None, max_length=20)
+    key = models.CharField(primary_key=True, default=None, max_length=50)
     value = models.CharField(default=None, max_length=50)
     class Meta:
         app_label = 'gui'