Groups of favorites lists in PhpStorm?

I develop a large PHP-based website with thousands of source files, and I make heavy use of the Favorites feature to create lists of the few source files involved in each enhancement I do, so as to easily go back to them if future enhancements are required.

After a year, I end up with dozens of favorites lists, and the 'Add to favorites' context menu is so tall some of the lists are cropped off. At the moment I'm forced to delete some lists to make more screen space available. I'd rather not have to do this.

What would be really useful is to be able to create a collapsible group of favorites - in my case I'd probably have groups called '2012', '2013' and '2014' - so as to reduce the screen footprint of the favorites list.

I don't think it's necessary to have multiple levels of nesting - one level would be enough.

Alternatively, is there another way to solve this problem (apart from deleting favorites lists, obviously)?

Thanks in anticipation,

Alan