Add a setting to not automatically close a pane when the last tab is closed

package.json

@@ -80,7 +80,7 @@
         "c9.ide.ace.split": "#0ae0151c78",
         "c9.ide.ace.statusbar": "#2155083cf6",
         "c9.ide.ace.stripws": "#cf0f42ac59",
-        "c9.ide.behaviors": "#ee32d7da73",
+        "c9.ide.behaviors": "#6530a20004",
         "c9.ide.closeconfirmation": "#cee4674141",
         "c9.ide.configuration": "#a9066299a2",
         "c9.ide.dialog.wizard": "#7667ec79a8",