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/Mod/Fem/App/FemConstraint.h

@@ -36,7 +36,7 @@ namespace Fem {
  * @brief Base class of all Constraint Objects of the Fem module.
  *
  * @details
- *  @ref Constraint isn't intended to be used directely. Actual Constraints
+ *  @ref Constraint isn't intended to be used directly. Actual Constraints
  *  used to specify a simulation are children of this class. The base class
  *  essentially does two things: Most importantely it has a property @ref
  *  Constraint::References which is a list of all sub objects the constraint
@@ -185,7 +185,7 @@ protected:
      *  index in normals[i].
      *
      * @param[out] points
-     *  For each vertex a point equal to the location of that vertix is pushed
+     *  For each vertex a point equal to the location of that vertex is pushed
      *  into the points vector. For each edge at least to points, the beginning
      *  and the end of the edge, are pushed into the vector. Depending on the
      *  length of the edge more points may be added in between. For each face a