Support for sub projects

Our product development group is divided into different focus areas with each focus area then having multiple different products that they develop. What we'd like to be able to do is create a high-level project for each focus area and then have a project per product underneath that high-level project. Each product could then have 1 or more repositories. So we'd like to see support for a project hierarchy of at least 2 levels added to Stash.

I did look at STASH-2727 which is for creating project categories - this may allow us to do something similar to what we need depending on how it was implemented and how permissions could be granted across categories.