Element.transform() now return a transform

added the overload for Element.transform() without arguments
Fix for #1921
Added support for svgjs.draggable
added callbacks

added callbacks methods for Element
added a test for Element.transform()

Test if svgjs.Element.transform() correctly return an svgjs.Element.Transform
defined the event type

this was not compiling because the event type was not defined
Merge pull request #1926 from LiFeleSs/master

svg.js Element.transform() now return a transform