Make RPK extraction path configurable (ideally within Maya Project)

[mistafunk]

Currently, RPKs are extracted to the system temp directory so renderers (Arnold) can access the textures. This is a problem if generation takes a along time (temp dir might be removed at reboot) or if the project has to be relocated to another machine.

Make the RPK extraction path configurable with the default location within the currently active Maya project.

[mistafunk]

Even better is to avoid RPK extraction altogether and copy the required textures into the maya project directory