[skip-ci] Various typo fixes

Found via codespell  v1.17.0.dev0  
```
codespell -q 3 -L aci,ake,aline,alle,alledges,alocation,als,ang,anid,ba,beginn,behaviour,bloaded,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,ist,kilometre,lod,mantatory,methode,metres,millimetre,modell,nd,noe,normale,normaly,nto,numer,oder,orgin,orginx,orginy,ot,pard,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
```

src/Mod/Assembly/App/AppAssembly.cpp

@@ -77,12 +77,12 @@ void AssemblyExport initAssembly()
     // call PyType_Ready, otherwise we run into a segmentation fault, later on.
     // This function is responsible for adding inherited slots from a type's base class.
  
-    // Item hirachy
+    // Item hierarchy
     Assembly::Item          ::init();
     Assembly::Product       ::init();
     Assembly::ProductRef    ::init();
 
-    // constraint hirachy
+    // constraint hierarchy
     Assembly::Constraint        ::init();
     Assembly::ConstraintGroup   ::init();
 }