Grasshopper Param

Some stuff I did at the weekend...

I basically just copied the *data type* and *param* implementation from Turtle. We need to decide whether this is okay to do and if so how to properly acknowledge the work done by Giulio Piacentino.

Note that I didn't make a ["proxy"][1] for Plankton, because I don't know what it is or why you need one!

Also, serialisation isn't implemented yet. Turtle handles the internalisation of ngon meshes just fine, so it's not something worth worrying about yet.

**Anyway...** the upshot of this is that Plankton's mesh feels much more native. It can exist as a *floating parameter* (new icon needed) and can automatically cast from a Rhino mesh. For instance, try plugging a Rhino mesh *directly* into the "DecomposePlankton" component.

[1]: https://github.com/piac/TurtleMesh/blob/master/TurtleGh/GH_TurtleMeshProxy.cs