Increase timeout for live docs

Note: it seems that this setting 'idle_timeout' is only used for live
documentation browser pages, so it should be safe to change it without
affecting users' worksheets' behavior.

sagenb/notebook/server_conf.py

@@ -14,7 +14,9 @@
 defaults = {'word_wrap_cols':72,
             'max_history_length':250,
 
-            'idle_timeout':120,        # 2 minutes
+            'idle_timeout':600,        # for a live documentation worksheet:
+                                       # quit the compute process if it has
+                                       # been idle for 10 minutes
             'idle_check_interval':360,
 
             'save_interval':360,        # seconds