Sort environment variables

Also add `GPG_TTY` to bash environment.
Fix 256color detection in terminal and Vim
Make tat support directories with periods

See: <https://github.com/thoughtbot/dotfiles/pull/281>
Add vim-gitgutter plugin

Also add a compatibility fix for the solarized colorscheme.

See: <https://github.com/airblade/vim-gitgutter/issues/164>.
Turn on colorcolumn by default