Bash: source ~/.shell_local for local variables
Bash: move config files to ~/.config/bash/
Bash: fix alias for `bashrc` on OS X

$VISUAL is 'mvim -f' on OS X, which means that the command won't return
until mvim is closed. We switch it to just directly use mvim.
Bash: rearrange order of sections in .bash_profile

This way, we set our shell settings before anything else, and then
immediately source our shell_local config (if it exists) to give it a
chance to override any settings that may come later.
Bash: only set $PROMPT_TEXT if not already set

Gives us a chance to set in in our ~/.config/bash/shell_local file.
Vim: remove duplicate Powerline init
Bash: in .bash_profile, convert tabs to spaces

This allows vim-indent-guides to have indent guides 1 column wide. With
tabs, the indent guides must be the same size as the tabstop.