[SQL Lab] Allow running multiple statements (#6112)

* Allow running multiple statements from SQL Lab

* fix tests

* More tests

* merge heads

* fix heads

superset/utils/decorators.py

@@ -0,0 +1,15 @@
+from contextlib2 import contextmanager
+
+from superset.utils.dates import now_as_float
+
+
+@contextmanager
+def stats_timing(stats_key, stats_logger):
+    """Provide a transactional scope around a series of operations."""
+    start_ts = now_as_float()
+    try:
+        yield start_ts
+    except Exception as e:
+        raise e
+    finally:
+        stats_logger.timing(stats_key, now_as_float() - start_ts)