Fix various (doxy) typos and whitespace issues

Found via `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,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/App/DocumentObject.h

@@ -123,7 +123,7 @@ public:
     /**
      * The function indicates whether the object type allows to define a view provider type
      * different than the standard type. The default implementation returns false.
-     * The function can be overriden by Python feature to return true where the type can be
+     * The function can be overridden by Python feature to return true where the type can be
      * retrieved from its proxy object.
      * \sa getViewProviderNameOverride()
      */
@@ -623,7 +623,7 @@ private:
     // accessed by App::Document to record and restore the correct view provider type
     std::string _pcViewProviderName;
 
-    // unique identifier (ammong a document) of this object.
+    // unique identifier (among a document) of this object.
     long _Id;
     
 private: