* Adds a PanelGroup class and slightly reworks the way panel
ordering is handled to fix bug 963550.
* Adds the option to load a python module containing
site customizations after the site is fully initialized,
but before the URLConf is dynamically constructed.
Fixes bug 965839.
Change-Id: Idc5358f2db6751494bcdfc382ec3bb6af65199b9