better export mesh as post-pro view

- new button under the graphic window to temporarily disable mouse
  selection (speeds-up redrawing of very large models + permits to
  rotate/zoom-in a model in selection mode even when the whole screen
  is full of selectable entities--e.g. a surface mesh)

- new "lasso" selection mode (to select entities using the same kind
  of lasso as the lasso zoom: just Ctrl+click, then drag the mouse in
  selection mode; the shortcuts are the same as for the lasso zoom)

- it is now possible to unselect entities using the middle mouse button
  (only for the creation of physicals at the moment; not sure if it's
  useful in the other cases)

- new button in visibility browser to invert the current selection
  (very useful e.g. when multiple physical entities are associated
  with a given elementary entity, in order to "peel" away the model
  when adding new physicals; cf. philou)

- changed meaning of Escape shortcut (cancel lasso or toggle mouse
  selection) + restore standard fltk Escape handling for all dialog
  windows

- updated copyright string

- new mesh label mode (coordinates); all label types are now also
  available for mesh vertices

- added option in 'Print Option' dialog to disable printing of help
  strings

- added a comment string with the date when creating a new file

- new snapping grid for adding points in the GUI

fix stat print for pyramids

replaced ExportLCField with ExportMeshStatistics (lc + gamma, eta, rho + elem num)

smaller lc files (%.16g -> %g)

- Generalized the "View" parser so that we can add new elements more easily
  (the code is *much* shorter, but unfortunately about 10-15% slower)

- Upgraded all post-pro file formats to handle curved (second order)
  elements: SL2, VL2, TL2, ST2, VT2, ... The new version number for the
  postpro files is 1.4

- Added code to automatically split the curved elements into linear
  elements when the view is created. WARNING: this is only a temporary
  solution: weshould generalize Adaptive_Post_View to handle these curved
  elements.

copyright update

generalized ExportLcField to all element types

The "Simplex" class is now derived from a new class "SimplexBase",
which contains only pointers to the nodes, and none of the other stuff
necessary for the actual mesh generation.

All the input/output/display routines have been rewritten in terms of
SimplexBase: this provides a gain of almost 50% in memory when you
just load meshes from .msh files to do visualization stuff, instead of
actually generating the mesh.

- added Orientation() members for hexas, prisms and pyramids

- use det3x3() instead of ad-hoc code everywhere it makes sense

- removed the quads from the simplex trees (finally...)

  **warning**

  this is a pretty big patch that touches a lot of different files. I
  tried my best to update all the things that needed to be updated,
  but I probably forgot some things... Please test! (especially the
  export routines in obscure formats like SMS, Gref, etc., as well as
  the extrusion code)

- added second order edge vertices for hexas, prisms and pyramids
  (drawing not done yet)

- added sanity check for number of values in post-pro parsed file
  format

- merged all mesh printing/reading routines in Print_Mesh.cpp and
  Read_Mesh.cpp

- cleaned up the statistics code