Add additional folder hierarchy to add support for submodules

Project mode lends itself to including a new type of component, the submodule.
Submodules are repositories that are already written by someone else and are free to be included in your projects. Example: Miyako has over 400 repos on his github account. You could grab some of files and include them in your project, but you lose one of the main features of a submodule: version tracking and updating.
The existing folder hierarchy does not seem to have a way to easily accommodate submodules.
When you install a submodule in a repo, you get the hierarchy of the submodule, including its own .git database, maybe a README file, a LICENSE file, etc.
It seems that a “submodules” folder, similar to “plugins” or “components” in a project would be useful. That would be a place for all your submodules to live, along with any resources that a submodule needs (forms, icons, sounds, methods, etc.)