refined arrow editor

adding test-case where 2nd order algo generates hanging nodes

Merged options->general->light panel into options->general->aspect. This
is more consistent with what we do in options->geometry and options->mesh.

don't print the full progname on batch info line

doc -convert

"gmsh -convert file file" now also translates meshes into the newest
format (in addition to parsed->binary post-processing views)

small fix to be more predictable

cleaner cut plane tests

- added little GUI for mesh cutting plane
- added option to draw the intersecting layer as surfaces

modify alt+shift+l to match the old behaviour

document second order simplices

- order 2 doc is done
- order 2 drawing is fone

added drawing code for faces of haxahedra, prisms and pyramids

removed the Mesh.Solid option: it's not necessary anymore

added drawing code for faces of 2nd order tets

Damn, "Palette" is defined in the Carbon API. Change it to "PaletteContinuous".

- allow to draw geometry tangents/normals even if the actual
lines/surfaces are not

- cleaned up draw_nonplane_surface

fixed (?) log scale for continuous maps (and maps where we don't check
for IntervalsType: scalar points, etc.)

restructured our rather liberal use of POLYGON_OFFSET_FILL (much better
now: it doesn't interfere with the glut primitives anymore)

simplified Draw_Simplex_Surface

use slightly larger arrows by default (60 pixels instead of 50)

more small cosmetic tweaks:

- don't display the big axes by default anymore (they're not as useful
  as they used to be, since we compute the rotations around the
  pseudo cog instead of the origin)
- set the default opengl font size to 12 (instead of 11)
- add some space between the scales and the labels (10 pixels instead
  of 5)

increase geom line width even more (2 pixels)

Refined mesh drawing code:

- draw surface element edges and/or faces
- draw volume element edges and/or faces
- consistent color choices between surface and volume elements
- wider geometry lines
- better defaults

better positioning of text labels on mesh and geometry

better test to check when to abort parsing