Move pm_list.set_click_handlers() call.

Instead of calling it from stream_list.initialize(), we
call it from the new pm_list.initialize().

static/js/pm_list.js

@@ -207,6 +207,9 @@ exports.update_dom_with_unread_counts = function (counts) {
 };
 
 
+exports.initialize = function () {
+    pm_list.set_click_handlers();
+};
 
 return exports;
 }());