incorrect file location when reference model is used

[craigmillernz]

In PF inversions, when a reference model is specified to be loaded from file, the output file location is used to load the reference model (which doesn't exist in that location), rather than the input file.

[domfournier]

Yep, that's probably a bug. I ll get to it.

[domfournier]

Will be addressed on GEOPY-78