fix STL export of quads

- replaced old 2nd order views with new adaptive stuff (still missing
  some function spaces for quads/hexas)

Added a sort of the eigenvalues and print functions

reorganized the API examples + show how you can build a new GUI using
the lib

  the .msh format -> bumped version from 2.0 to 2.1)
- move createTopologyFromMSH into GModel.cpp (and renamed to
  createTopologyFromMesh)

added createTopology when Merging a MSH File and implemented discreteEdge

interpolation (which prevent geo transforms on extruded entities)

- display all control points in GUI for gmsh curves
- uniformize Fl_Value::step() values in GUI

instead of implementation details (tetgen+delaunay & co)

- simplified background drawing (+added option to use jpeg/png image)
- better default clipping planes

a script, and when this size was different than the current size, it was
impossible to make the window larger)