Backport PR #5803: unify visual line handling

Extra change on top of @ivanov pr  #5768 to have more consistent handling of visual lines.

In a  long wrapped line End/Cmd-Right will go to the end of the visual line which seem more logical.
Cmd-Left beginning of line. I did note rebind Ctrl-Left because there is already custom logic in code mirror for "smart" beginning of line.

IPython/html/static/notebook/js/cell.js

@@ -70,7 +70,12 b' var IPython = (function (IPython) {'
         cm_config : {
             indentUnit : 4,
             readOnly: false,
-            theme: "default"
+            theme: "default",
+            extraKeys: {
+                "Cmd-Right":"goLineRight",
+                "End":"goLineRight",
+                "Cmd-Left":"goLineLeft"
+            }
         }
     };