feat(api): split api into multiple apps (#1626)

Fixes #1622

- split the api into 4 apps: core, history, schedule, storage
- exploded the settings into testing/prod

api/libretime_api/core/serializers/user.py

@@ -0,0 +1,20 @@
+from django.contrib.auth import get_user_model
+from rest_framework import serializers
+
+
+class UserSerializer(serializers.HyperlinkedModelSerializer):
+    class Meta:
+        model = get_user_model()
+        fields = [
+            "item_url",
+            "username",
+            "type",
+            "first_name",
+            "last_name",
+            "lastfail",
+            "skype_contact",
+            "jabber_contact",
+            "email",
+            "cell_phone",
+            "login_attempts",
+        ]