Added point pad to middle of links, links can now connect to links. All connections are now based on pads

Added Scrolling to DiagramWidget example, made ForceRefresh local to diagramwidget

Added binding to anchored text; Made Node and Link extensible; Fixed handles so that resizing does not move node

1) Removed Refresh() call from AnchoredText MouseIn and MouseOut functions.
2) Changed DiagramWidget so that the renderer's objects come back in an ordered sequence (random ordering was the cause of the flicker). This required changing the widget's representation of the inventory of diagram elements to a linked list, which in turn required a number of modifications to functions involving lists of Nodes and Links.

Static check error fixed; Fixed rotating arrow heads

This reverts commit 3be0276.

Fixed arrowhead rotation. It wasn't a problem with fyne 2.3.5, but would have been a problem with fyne 4.0. Now it won't be a problem.
Made DrawingArea public to support application-level testing scenarios that require simulated Drag, Mouse, and Tap events to be sent to the diagram.
Made (but commented out) a change to AnchoredText for fyne 2.4.0 so that anchored text does not scroll. This needs to be uncommented for fyne 2.4.0