Add Unite modules and dependencies

- neomru for MRU list sources
- vimproc for async actions
- unite-outline for an outline source
Add Unite.vim configuration + key maps
Add some cool Unite usages

- Git actions menu
- Quick access to Rails paths
Remove NERDTree plugin, commented out plugins
Add vim-rails plugin and some shortcuts
Remove commented-out vim-visual-star-search plugin
Fix vim-airline showing up

As per http://git.io/AOUOUg