renderer.CanvasHandler.canvasSizeChanged(): added propagation of resize event

Now we can register a listener on the xml3d element for "resize". The event's
detail will hold an object with properties width and height.
interface-elements: removed a wrong return statement
Critical Xflow fix.
Implemented Xflow operator overloading.

There can now be several operators with the same name.
Operators with matching input types is choosen.
If no operator matches, a detailed list of all operators
Merge branch 'xflow-overloading' into develop
Added an option for movement aware click handling. When TRUE a click event will not be triggered if the mouse has moved more than 4 pixels between the mousedown and mouseup events. Default is FALSE.
Added a function to create a XML3D.math.bbox out of a XML3DBox
Issue #62: Added a public interface to set the world space bounding box of an object
Merge branch 'develop' of https://github.com/xml3d/xml3d.js into develop