Changing the source/target arc location changes both start and end
locations

* When moving a source the targets end point was not updating to the new
  location and vice versa
* Set change listener to calculate start and end for any updates
* Added unit tests
Pop ups for components positions are now relative to component not mouse
point

* This fixes the arc point pop up being somewhere else
:wq
Deleting arc point deletes the right one

* Problem was that arcpoints equal method was set to return true
Arc view  updates source/end points on intermediate point deletion