Fix bug when renaming data

If user want to rename a data from GUI, result was

  Traceback (most recent call last):
    File ".../oalab/src/openalea/oalab/project/projectwidget.py", line 516, in rename
      self._rename(project, category, name)
    File ".../oalab/src/openalea/oalab/project/projectwidget.py", line 504, in _rename
      renamer = RenameModel(list_models, name)
    File ".../oalab/src/openalea/oalab/project/projectwidget.py", line 100, in __init__
      self.combo.setCurrentIndex(self.models.index(model_name))
  ValueError: u'sample.jpg' is not in list

This pull request fix this issue