fix 'SaveAs' in case of overwriting existing project

Traceback (most recent call last):
File "/home/developer/WorkData/PLC/beremiz/beremiz/BeremizIDE.py", line 959, in OnSaveProjectAsMenu
self.CTR.SaveProjectAs()
File "/home/developer/WorkData/PLC/beremiz/beremiz/ProjectController.py", line 600, in SaveProjectAs
self.SaveProject(old_project_path)
File "/home/developer/WorkData/PLC/beremiz/beremiz/ProjectController.py", line 579, in SaveProject
self._getProjectFilesPath(self.ProjectPath))
File "/usr/lib/python2.7/shutil.py", line 200, in copytree
os.makedirs(dst)
File "/usr/lib/python2.7/os.py", line 157, in makedirs
mkdir(name, mode)
OSError: [Errno 17] File exists: '/tmp/tests/project_files'

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#EDE (Engineering-Data-Exchange) - generated by Beremiz BACnet plugin;;;;;;;;;;;;;;;

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PROJECT_NAME;%(Project Name)s;;;;;;;;;;;;;;

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VERSION_OF_REFERENCEFILE;%(EDE file version)d;;;;;;;;;;;;;;

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TIMESTAMP_OF_LAST_CHANGE;%(Current Time)s;;;;;;;;;;;;;;

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AUTHOR_OF_LAST_CHANGE;%(Project Author)s;;;;;;;;;;;;;;

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VERSION_OF_LAYOUT;2.1;;;;;;;;;;;;;;

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#mandatory;mandatory;mandatory;mandatory;mandatory;optional;optional;optional;optional;optional;optional;optional;optional;optional;optional;optional

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#keyname;device obj.-instance;object-name;object-type;object-instance;description;present-value-default;min-present-value;max-present-value;settable;supports COV;hi-limit;low-limit;state-text-reference;unit-code;vendor-specific-address