Changes for 2.0.19

Note: these bugfixes will be incorporated into the 2.1 branch as part of the upcoming 2.1.1 release.

• Fixed Model.fromJson loading models with serialized EnumValues.
• Improved showing non-default cursors when dragging between diagrams.
• Fixed the operation of Diagram.handlesDragDropForTopLevelParts when dragging on the elements of a Group.
• Fixed a bug where Diagram.scrollHorizontalLineChange and Diagram.scrollVerticalLineChange would not affect scrolling size in some browsers.
• Fixed a bug where some AvoidsNodes Links would not route properly in nested groups.