Improve vim statusline, remove powerline

This makes the statusline more useful without a heavy (and currently
broken for me) plugin. Taken from Wincent:

  https://github.com/wincent/wincent/blob/master/.vim/plugin/statusline.vim
Wrap remove trailing whitespace autocmd in augroup

This prevents it from doubling up if the file is re-sourced. More
information at:

  http://learnvimscriptthehardway.stevelosh.com/chapters/14.html
Automatically disable paste mode when leaving insert

When pasting content, I usually only want to paste once, and then turn
off paste mode. The process typically looks like this:

  :set paste
  i<C-v><ESC>
  :set nopaste

This commit adds an autocmd that automates the last step of this. This
may end up being annoying in the instance where I want to paste multiple
things, but I am having a hard time recalling when I have actually
wanted to do that at this time so I'm not going to worry about it.
Add more vim abbreviations

These are some common typos that I make, so I'm adding them to my vim
abbreviations to prevent them from being made again.