Add model management and database

- use sqlalchemy + alembic + sqlite for db
- extract model data and previews
- endpoints for db interactions
- add tests

utils/web.py

@@ -0,0 +1,12 @@
+import json
+from datetime import datetime
+
+
+class DateTimeEncoder(json.JSONEncoder):
+    def default(self, obj):
+        if isinstance(obj, datetime):
+            return obj.isoformat()
+        return super().default(obj)
+
+
+dumps = DateTimeEncoder().encode