Returns the full path to the project's assets.
If called from a regular Julia session it will just return the supplied argument augmented with "/assets/"
However, if called from a session compiled using PackageCompiler it will return the path to the assets subfolder in the packaged app.
Used in the build step of a new app created using PackageCompiler. Copies all assets from pkg to the new app.
Returns true if called from a standard Julia session. False if called from an app created using PackageCompiler.