[MCT-3811] Fix for Canvas on canvas: Panel cannot be
selected, drag-drop throws exception.
Fixed the issue of selection of panel with a canvas. The issue was
that the selection was cleared by a call to panel.clearSelections. Moved
this call in front of the panel selection. 
Fixed the exception when performing a DnD of the canvas panel in the
canvas. An endless loop was initiated between panel and canvas for
selection changes when clearing selections. Now testing whether
any selection needs to be cleared, if not, no clearing is initiated
preventing the infinite loop.