Add vim-gitgutter plugin.

vim-gitgutter - A Vim plugin which shows a git diff in the 'gutter'
(sign column). It shows whether each line has been added, modified, and
where lines have been removed. You can also stage and revert individual
hunks.  [Source](https://github.com/airblade/vim-gitgutter).
Add vim-airline plugin.

vim-airline - Lean & mean status/tabline for vim that's light as air.
[Wiki](https://github.com/bling/vim-airline/wiki).
[Source](https://github.com/bling/vim-airline).
Add Syntastic plugin.

Syntastic is a syntax checking plugin for Vim that runs files through
external syntax checkers and displays any resulting errors to the user.
This can be done on demand, or automatically as files are saved. If
syntax errors are detected, the user is notified and is happy because
they didn't have to compile their code or execute their script to find
them.  [Source](https://github.com/scrooloose/syntastic).
Reorder plugin list
Remove cruft