Grace period strategy for unloading projects

Today, navigating to a file in another project might involve a full project load. Bad! Users often navigate back to the original project, and then dive right back into the loaded project. Unfortunately, by the time that they do that, that project is unloaded and all the work has to be done **all over again**. We might want to consider something like a "grace period" for unloading projects when the last open file of a project is closed.