Compatibility highlight

This is something I have been experimenting with. I wanted to be able to give visual feedback to indicate if a certain node item input is compatible with another output (or vice versa).

This is achieved by supplying an instance of an `ICompatibilityStrategy` to the graph control. This should allow for a high amount of customizability.
One example strategy I supplied it the `TagTypeCompatibility` strategy, which simply compares the type of the `Tag` property that is assigned to a node item. I also adjusted the example application to showcase how this works.

I left this behavior disabled by default.