Fix typos, grammar, and some whitespace issues

Found via `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/View3DPy.cpp

@@ -192,7 +192,7 @@ void View3DInventorPy::init_type()
         "noManip: whether to create a manipulator\n"
         "pla: clipping plane placement");
     add_varargs_method("hasClippingPlane",&View3DInventorPy::hasClippingPlane,
-        "hasClippingPlane(): check whether ths clipping plane is active");
+        "hasClippingPlane(): check whether this clipping plane is active");
 }
 
 View3DInventorPy::View3DInventorPy(View3DInventor *vi)