unify exception handling of Beremiz and PLCOpenEditor

fix problem running PLCOpenEditor

$ ./PLCOpenEditor.py
../src/common/stdpbase.cpp(62): assert "traits" failed in Get(): create wxApp before calling this

Regression was introduced by '3311eea' (clean-up: fix PEP8 E402 module level import not at top of file)

don't check any particular wx version

Beremiz works with any version of wx.

fix problem when Beremiz is running without matiec installed

set matiec settings only once on first use of ProjectController class and give
user-friendly message on compilation about missing matiec
installation.


Traceback (most recent call last):
File "Beremiz.py", line 197, in <module>
beremiz.Start()
File "Beremiz.py", line 192, in Start
self.CreateApplication()
File "Beremiz.py", line 130, in CreateApplication
self.BackgroundInitialization()
File "Beremiz.py", line 137, in BackgroundInitialization
self.ImportModules()
File "Beremiz.py", line 176, in ImportModules
import BeremizIDE
File
"BeremizIDE.py", line 76, in <module>
from ProjectController import ProjectController, GetAddMenuItems,
MATIEC_ERROR_MODEL, ITEM_CONFNODE
File
"ProjectController.py", line 177, in <module>
iec2c_cfg = Iec2CSettings()
File
"ProjectController.py", line 101, in __init__
self.ieclib_c_path = self.findLibCPath()
File
"ProjectController.py", line 135, in findLibCPath
os.path.join(self.ieclib_path, "C"),
File "/usr/lib/python2.7/posixpath.py", line 70, in join
elif path == '' or path.endswith('/'):
AttributeError: 'NoneType' object has no attribute 'endswith'