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'

Project overview
================

In order to target the widest possible range of programmable devices and keep efficient, Beremiz use C code as an intermediate language. 

To be executed, C needs to be compiled. `GCC <http://gcc.gnu.org>`_ serve that purpose perfectly.

PLC program is expressed in languages defined in IEC-61131, including graphical languages. Thanks to PLCopen TC2, those graphical languages have a standardised representation, in XML.

To be continued.