- this fixes a mistake from commit ef088674
- it also consistently use the thermal expansion coefficient
- add code comments
now the material task dialog works with all fluid materials without errors or warnings
- since a while ThermalExpansionCoefficient is used, VolumetricThermalExpansionCoefficient is only used for the material task panel
- as already stated in a code comment, the unit of VolumetricThermalExpansionCoefficient is ThermalExpansionCoefficient, therefore we must check for ThermalExpansionCoefficient
- we must also check if ThermalExpansionCoefficient exists
- Adapt the existing fluid material cards to use the ThermalExpansionCoefficient
Found via `codespell -q 3 -L aci,ake,aline,alle,alledges,alocation,als,ang,anid,apoints,ba,beginn,behaviour,bloaded,bottome,byteorder,calculater,cancelled,cancelling,cas,cascade,centimetre,childs,colour,colours,commen,connexion,currenty,dof,doubleclick,dum,eiter,elemente,ende,feld,finde,findf,freez,hist,iff,indicies,initialisation,initialise,initialised,initialises,initialisiert,inout,ist,kilometre,lod,mantatory,methode,metres,millimetre,modell,nd,noe,normale,normaly,nto,numer,oder,ontop,orgin,orginx,orginy,ot,pard,parms,pres,programm,que,recurrance,rougly,seperator,serie,sinc,strack,substraction,te,thist,thru,tread,uint,unter,vertexes,wallthickness,whitespaces -S ./.git,*.po,*.ts,./ChangeLog.txt,./src/3rdParty,./src/Mod/Assembly/App/opendcm,./src/CXX,./src/zipios++,./src/Base/swig*,./src/Mod/Robot/App/kdl_cp,./src/Mod/Import/App/SCL,./src/WindowsInstaller,./src/Doc/FreeCAD.uml,./build/doc/SourceDocu`
