Refactor czi_hosted and server into backend directory, pull common code into backend/common, refactor tests (#2102)

* move local_server -> backend/server server-> backend/czi_hosted, pull common code into backend/common update imports, tests and make commands

backend/czi_hosted/db/create_db.py

@@ -0,0 +1,18 @@
+"""
+Drops and recreates all tables for local testing according to cellxgene_orm.py
+"""
+from sqlalchemy import create_engine
+
+from backend.czi_hosted.db.cellxgene_orm import Base
+
+
+def create_db(database_uri: str = "postgresql://postgres:test_pw@localhost:5432"):
+    engine = create_engine(database_uri)
+    print("Dropping tables")
+    Base.metadata.drop_all(engine)
+    print("Recreating tables")
+    Base.metadata.create_all(engine)
+
+
+if __name__ == "__main__":
+    create_db()