Staging resources for development

[weefuzzy]

Developing and debugging in PD is a bit of a pain because of the need to gather together externals, helpfiles and whatever else into a single flat folder.

One thing to try might be to add a special set of CMake install targets with a specific component type ('development' or something), excluded from the default install. These targets could then be used to construct a flat folder of symlinks in the build tree. If new targets or files were added, it would need running again, but at least for iterating on a particular object it should work as something to point PD at.