fix: Fix welcome email bugs

Send only when new user is created
Require email address when user created

Resolves #32

people/migrations/0018_require_user_email.py

@@ -0,0 +1,18 @@
+# Generated by Django 2.2.10 on 2020-05-28 15:17
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('people', '0017_answerset_replaced_timestamp'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='user',
+            name='email',
+            field=models.EmailField(max_length=254, verbose_name='email address'),
+        ),
+    ]