Deprecating coala-vim in favour of syntastic

Syntastic does seem to look pretty promising. It's well-documented. The interface looks good and it does the job. The plugin itself has proper support and works with all the major plugin managers on vim.
It'll need a PR to be added as a checker in syntastic, enabling it to be used (to my understanding at the moment). Also the `vimrc` will have
`let g:syntastic__checkers = ['']`
So we'd have it under several filetypes I suppose.

Ref:
https://github.com/vim-syntastic/syntastic