- lots of improvements to the dimention display : closes #127
 * position of dimentions is more coherent
 * added arrows/lines etc for more clear display of dimentions
 * added a new custom arrowHelper, with fixed size arrows for the above
 * some clean up
- added volume calculation based on http://stackoverflow.com/questions/1410525/volume-of-a-3d-closed-mesh-car-object
 * this is towards #128
 * seems ok , but precision is not perfect (accumulation of errors)
 * just dumped to the console on object selection, needs ui
- display of volume works correctly : closes #128
 * just click on the info icon on a selected object to display it
 * now only gets computed on first click, then stored in the mesh

- various related cleanups and bugfixes in the visual Editor and helpers
 * selectionHelper refined : now uses the THREE.js event dispatch mechanism : this is hooked up to the dom overlay to display infos about selected objects
 * also now used for cleaned up selection process
 * removed the need for renderCallback for selection and hover
 * fixed background color setting to work with composer aswell (setting bg color in the renderer)
 * fixed bug with geometries that did not have their bounding box computed, which caused some issues on selection
 * various additional cleanups in selection helper
 * various cleanups in the visualEditor