Fix typos in various files [skip-ci]

Found via `codespell 2.0.dev0`  
```
codespell -q 2 -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,currenty,dof,doubleclick,dum,eiter,elemente,feld,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/Gui/Tree.cpp

@@ -1710,7 +1710,7 @@ void TreeWidget::dropEvent(QDropEvent *event)
                 vp = Base::freecad_dynamic_cast<ViewProviderDocumentObject>(
                         Application::Instance->getViewProvider(targetObj));
                 if(!vp) {
-                    FC_ERR("Cannot find drop traget object " << target);
+                    FC_ERR("Cannot find drop target object " << target);
                     break;
                 }