Packages

With this change, the PM will scan template directories for a `template.xml` file in the template root (e.g. `Full/template.xml`). This file determines which of the packages in the `Packages` directory next to the PM executable should be included when a new project is created from the template.

Currently, when you create a new project, the PM just copies the contents of the template you've chosen into the project folder. Now, it will _also_ copy the contents of every package named in `template.xml` with `inclusion="required"` or `inclusion="recommended"`. This means we can separate commonly-used bits of template out into packages, and include them by referring to them in `template.xml`.

This should have no effect on current project creation. There are also no UI changes.