Minor changes

Hi Daniel,

I've added a *.gitignore* file to the repository (taken from [here](https://github.com/github/gitignore/blob/master/VisualStudio.gitignore)) and have removed some files/folders from the repository accordingly. Basically, anything that can be generated (e.g. build output) or user specific configurations (e.g. *.user files) don't need to be in the repo.

I also found a small issue with the project reference in *PlanktonComponents* that was preventing the project from building unless I checked it out into a folder called *"HalfEdgeMeshLibrary"* (by default when cloning a git repository the folder name is the name of the repository, i.e. *"Plankton"*...).

Just small stuff to begin with, but there's more to come!

All the best,

Will