- Removed Powerline usage (Bash, Vim and tmux), was more convoluted and

less portable than customizing the prompt myself.
- Symlink the TravisCI Bash completion to the one generated by the
travis gem inside .bash_completion.d, remove specific source in .bashrc.
- Moved AWS CLI completion to file inside .bash_completion.d.
- Removed some unused blocks in .bashrc.