FEM: Add "None" and simplify material setting

The "-->choose Material" has been replaced with a not defined material.
That makes setting/retrieving material to/from the object much easier
and allows user to have a "not defined" material. Previously it wasn't
possible to change i.e. form Steel to "not defined".

Signed-off-by: Przemo Firszt <przemo@firszt.eu>

src/Mod/Material/CMakeLists.txt

@@ -14,6 +14,7 @@ SOURCE_GROUP("Module" FILES ${Material_SRCS})
 #FILE( GLOB MaterialLib_Files ./StandardMaterial/*.FCMat ./StandardMaterial/*.txt  )
 
 SET (MaterialLib_Files
+    StandardMaterial/None.FCMat
     StandardMaterial/ABS.FCMat
     StandardMaterial/CalculiX.FCMat
     StandardMaterial/Concrete.FCMat

src/Mod/Material/StandardMaterial/None.FCMat

@@ -0,0 +1,27 @@
+; Standard Not Defined Material
+; (c) 2015 Przemo Firszt (CC-BY 3.0)
+; information about the content of such cards you can find here:
+; http://www.freecadweb.org/wiki/index.php?title=Material
+
+[General]
+Name = None
+Father = None
+; more elaborate description of this material card:
+Description: This is a not defined material
+; Specific wight in kg/mm^3 
+SpecificWeight = 0.0
+; No special Vendor
+Vendor:
+; For blend materials the wikipedia page is a good source of information:
+ProductURL =
+; for blends a rough estimation  Euro/Kg
+SpecificPrice = 0.0
+
+[Mechanical]
+; youngs modulus (or E-Module or Modulus of Elasticty) (source: http://en.wikipedia.org/wiki/Young%27s_modulus)
+YoungsModulus=0 MPa
+; http://en.wikipedia.org/wiki/Ultimate_tensile_strength in 
+UltimateTensileStrength= 0 MPa
+
+[FEM]
+PoissonRatio = 0.0