Fem: add _CommandMaterialFluid.py and FemMaterial.makeFluidMaterial

[qingfengxia]

Continue on Bernd's re-factoring work, I add the makeFluidMaterial() method and fluid material command class into Fem. Cfd workbench will import them directly

The FluidMaterial taskpanel ui is redesigned, but py coding is yet done, but it does not break existent code and case. Team of CSIR can merge their code into the _TaskPanelFemMaterial.py by a switch like

if obj.hasProperty('Category') and obj.Category == 'Fluid':
    # fluid material code 

see my last post [Re: How about a general FemMaterial.py to suport Mechancial, Thermal, Fluidic and ElectroMagnetic]http://forum.freecadweb.org/viewtopic.php?f=18&t=19401&p=152379#p152379

[wwmayer]

Please check that the build is broken on all systems because the unit tests fail:
`

ERROR: test_new_analysis (TestFem.FemTest)

Traceback (most recent call last):
File "C:\projects\freecad\build\Mod\Fem\TestFem.py", line 200, in test_new_analysis
self.create_new_material()
File "C:\projects\freecad\build\Mod\Fem\TestFem.py", line 112, in create_new_material
self.new_material_object = FemMaterial.makeFemMaterial('MechanicalMaterial')
AttributeError: 'module' object has no attribute 'makeFemMaterial'

ERROR: test_new_analysis (TestFem.TherMechFemTest)

Traceback (most recent call last):
File "C:\projects\freecad\build\Mod\Fem\TestFem.py", line 458, in test_new_analysis
self.create_new_material()
File "C:\projects\freecad\build\Mod\Fem\TestFem.py", line 365, in create_new_material
self.new_material_object = FemMaterial.makeFemMaterial('MechanicalMaterial')
AttributeError: 'module' object has no attribute 'makeFemMaterial'

Ran 84 tests in 17.651s
FAILED (errors=2)
`

[qingfengxia]

Sorry, I always forget the test Suit. TestFem.py