Setup bash with powerline as a fallback to xonsh

[andreoliwa]

xonsh is not 100% stable, so sometimes I need to go to bash and run things from there.

• [x] Research powerline
• [x] Setup a proper .bashrc symlink
• [ ] Rename an existing .bashrc to .bashrc-<current timestamp> Not now
• [x] Check all roles and see which ones need to be in .bashrc (e.g. pyenv)
• [ ] Maybe source all .sh files from ~/dotfiles, similar to what zsh and xonsh do? Not now