Medcat conversion mode name hotfix

[mart-r]

This fixes 2 small issues with converted model names:

• If it's a .zip, the previous implementation would leave teh .zip in the middle of the new name
  • That's because the save mechanism adds the hash and extension (unless otherwise specified)
• If it's a folder, the converter would fail
  • Because the old_model_name attribute wasn't set

EDIT: This is an extension of #118