Removing nerdtree

I'm trying to get off of the [project drawer][1] setup.

[1]: http://vimcasts.org/blog/2013/01/oil-and-vinegar-split-windows-and-project-drawer/
Add vim-vinegar[1]

I'm going to give it a try over nerdtree

[1]: https://github.com/tpope/vim-vinegar
Merge in switch from nerdtree to vim-vinegar