Make the exported folder portable

I do use a computer with Photoshop to export with Photoshop Exporter.

As I develop on Linux I would like to import the result from my Linux machine.

As of today, metadata file use absolute paths so one cannot move the exported folder from Qt Bridge Photoshop plugin somewhere else (different path or different machine).

 Solution would be to make paths relative to the exported folder so one can move it anywhere (e.g to another machine).