Implement resource location based on Paths vs mobile

[ivanperez-keera]

The Paths mechanism provided in cabal for normal packages does not currently work on mobile. It's been disabled for the whole game in the feature-sage branch.

There should be a way around this. For resources, one could have a resource "Locatable" instance in the package that implements the right approach during compilation, and is only expressed with type constraints in libraries.

[ivanperez-keera]

It might also be possible to just provide a Paths module with the same interface as Paths_package, which exports the latter on PC/Mac and implements the right substitutions in iOS/Android.

SDL has its own mechanism, which may also get in the way.