Support for "templated" workspace creation

[GeorgeLyon]

It would be cool if you could have a template for creating a new workspace, using which could be as easy as git clone http://josh/central.git:workspace-from-template=path/to/template-spec/new-module-name. This would be useful for situations where a project has many similarly-structured modules, like screens of an app or handles of a server process.

For a bit more detail, imagine a project with the following structure:

<root>
  ├─ Project.project-file
  ╰┬ Submodules
   ├┬─ josh-template
   │├── workspace.josh
   │╰── %josh-template%.subproject-file
   ├┬─ Submodule A
   │├── workspace.josh
   │├── SubmoduleA.subproject-file
   │╰┈
   ╰┬─ Submodule B
    ├── workspace.josh
    ├── SubmoduleB.subproject-file
    ╰┈

It would be cool if we could "clone" SubmoduleC and have josh create the subdirectory structure for us from josh-template (possibly as simple as replacing instances of %josh-template% in file names and contents, but maybe more configurable). Without this functionality, the only thing to do would be to clone the whole repo, or have a special "Create a new submodule" workspace.

The creation operation probably shouldn't commit to the repo, so it may make sense to piggy-back on another git clone argument: (maybe something -b josh-create-from-template:<branch-name>)