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'

<?xml version='1.0' encoding='utf-8'?>
<PyFile xmlns:xhtml="http://www.w3.org/1999/xhtml" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <variables/>
  <globals>
    <xhtml:p><![CDATA[

/*
    Web interface is build as SVG file in Inkscape. 
    To edit SVG file click 'Inkscape' button on the toolbar above.
    
    Inkscape is a free and open-source vector graphics editor. 
    It's not part of Beremiz and needs to be installed separately.
*/

]]></xhtml:p>
  </globals>
  <init>
    <xhtml:p><![CDATA[
]]></xhtml:p>
  </init>
  <cleanup>
    <xhtml:p><![CDATA[
]]></xhtml:p>
  </cleanup>
  <start>
    <xhtml:p><![CDATA[
]]></xhtml:p>
  </start>
  <stop>
    <xhtml:p><![CDATA[
]]></xhtml:p>
  </stop>
</PyFile>