** Requires update to Unity branch **
- New way to reference StyleSheets (no longer using attributes). This in the
goal of moving GraphView to a GitHub submodule.
- Styles sheets moved under Resources folder
- BaseTypeMapper renamed BaseTypeFactory
- Little change to edge drawing code.
- Changes to selection mechanism.
- NodeAnchors are no longer always removed/added on a DataChange (more changes
to come to this soon).
- Dragger and NodeDragger change only the VisualElement on MouseMove. The
presenter is now changes and notified of the change only upon MouseUp.
- Various minute changes to demo presenters.
Signed-off-by: joce <joce@unity3d.com>