Using filter to ignore invisible elements in hit testing on design surface.
Some fixes to BorderForInvisibleControl adorner as follows;
Only shows the adorner panel if the parent component is visible.
If component is a ContentControl it must be of type ContentControl specifically, and not derived types like Label and Button where the added border is not wanted.
If component is a Border the adorner border is only drawn on the edges that is invisible.
The adorner is only created the first time it is added to adorners collection.
Movement of a control is now only possible if the control is visible.
Previously you could move an element that was hidden by hovering the cursor on the edges of the hidden control, and clicking when you saw the move-cursor appear.
Merge pull request #70 from gumme/WpfDesignerFixes

Wpf designer fixes