Release of VEMLAB 2.4

>>  From VEMLAB 2.3 to VEMLAB 2.4:

• Add several options for in plot_and_output_options.m. New options: delete existing output files, plot front/isometric view of the figure, print and save pdf figures, save .fig figures, set figure resolution, color system for the colorbar, colorbar ticks and lines, figure ticks, figure grid, set min/max limit of the colorbar.
• Several enhancements to the output figures.
• Improvements for plotting of FEA results on FEM2DQ4 elements.
• Add several example test problems in “test” folder.
• Create a polygonal mesh from a 3-node triangular mesh (see folder “mesher”).
• Three stabilization options are now available in LinearElastostatics module.
• Mesh size parameter is now computed as the average area of the polygons in the mesh.
• Update VEMLAB Primer.