added notebook_mode file

openmdao/core/notebook_mode.py

@@ -0,0 +1,23 @@
+"""Checking for interactive notebook mode."""
+
+
+def _notebook_mode():
+
+    try:
+        from IPython import get_ipython
+        ipy = get_ipython() is not None
+    except ImportError:
+        pass
+    else:
+        try:
+            import tabulate
+        except ImportError:
+            print("Tabulate is not installed run `pip install openmdao[notebooks]` to install "
+                  "required dependencies")
+    return ipy
+
+
+if _notebook_mode():
+    notebook = True
+else:
+    notebook = False