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