Rename projects (and namespaces)

* HalfEdgeMeshLibrary -> Plankton
* PlanktonComponents -> PlanktonGh
Split classes in Plankton.cs into separate files and rename

* one file per mesh element class
* rename (for example) P_mesh -> PlanktonMesh to better follow C# naming
* All instances of `HalfEdge' renamed to `Halfedge' (it was bugging me for some reason)
Tidy up (whitespace changes only)

Just tidied up PlanktonMesh.cs (well, SharpDevelop did...) while I was working on it. Figured I should commit the whitespace changes first to avoid muddying the waters in the next commit.
Create PlanktonMesh from face-vertex representation

* new AddFace method follows the process described in OpenMesh's PolyConnectivity class
* Handles creation of any missing halfedge pairs and ensures halfedge data structure (HDS) is always correctly linked (next/prev/etc.)
Add test project
Update solution to include test project