and yet more css and layout changes for dialogs
- various additions and improvements to the 3d view:
 * added experimental "structural" rendering (see through with hashed lines for backfaces) closes #97
 * better object rendering style switching implemented (shaded/wireframe/structural)
 * added settable positioning for grid numbering (center or grid border) , refactored/improved the grid helper : closes #96
 * fixed #95 : grid shadowing issue (was simply a spotlight (shadow caster) distance issue)