Added an option to set the number of subdivisions used when drawing
spheres (when geometry, mesh or post-processing points are drawn as 3D
spheres). You can test with:

gmsh tutorial/t5.geo -string "Geometry.PointType=1; Geometry.PointSize=8; General.SphereSubdivisions=10;"

Add some comments on the TWO_FACE lightning bug. To be fixed later.

normals. This caused the blurred stuff when changing time steps...

right-clicking on the view button (which nobody found without asking
me... and was not easily available on Macs with 1 button mice), there
is now a small arrow (with a tooltip) next to the view
button. Clicking on this arrow pops up the option menu.

Change default post-processing iso mode to continuous map. The old default value just confused too many people doing 3D stuff.

- "OK" is to agree with what in the dialog *AND* close the dialog
- "Apply" is to apply the current values selected in the dialog, but
   leave the dialog open
- "Cancel" is to close (hide) the dialog and *NOT* apply the
   changes that might have been made in the dialog

Also increased default width of buttons