preparing for drag'n'drop: moved code from mouseClicked to mouseReleased
changed name of clickedNode to draggedNode, changed its scope
added drag handler, fixed code that selects note upon double click
implemented dragging
cleaning: renamed variables
cleaned, added comments
removed unnecessary output
implemented forward dragging (within same layer of nodes)
simplified code
moved drag and drop code to separate method
fixed bug: dragging to root no longer allowed
added commentation
Merge branch 'devel'