Smooth.h

- First draft (pretty much untested!) of new "Integrate" plugin to
  * integrate scalar fields over all the elements in a view
  * integrate the circulation of vector fields along line elements
  * integrate the flux of vector fields across surface elements

  Used with Plugin(DisplacementRaise) and Plugin(Evaluate) this
  permits for example to compute the area/volume of deformed
  configurations; and, with Plugin(CutPlane)+Plugin(Skin), the
  perimeter of deformed sections. Another interesting application is
  to use it on a vector field with Plugin(CutPlane), in order to
  compute fluxes across arbitrary cross-sections.

- Added "connectPoints" option to Plugin(CutParametric) so
  that we can feed its output to Plugin(Integrate)

- Added Normals and Tangents options to visualize the orientation of
  elements in post-processing views

- Added "swapOrientation" in Plugin(Transform) to change the
  orientation of the elements (in place) (+ moved the transformation
  routines from the view class into the plugin)

- fixed #defines in some of the plugin header files