- continued work on dimensions display:
 * cleaned up code
 * added position and orientation to SizeArrowHelper so it can be used more easilly for
the dimensions helper

- added slight effect when dealin with a scene with multiple objects : the current selection stays
as it is, other objects get a lowered opacity: this helps with focusing on selection
- refactored/ extracted a number of visual helpers into their seperate files

- inverted left/right rotate on screen controls
- fixed offset issue with dimensions helper