Add autoenv and youtube-dl to bash

The autoenv and youtube-dl repos are added as submodules under
`shell/bash/extra`.

The `shell/bash/bashrc` file is updated to source the autoenv activation
script and to create an alias to `youtube-dl`.
Update files in `shell/common.d`

Add functions and aliases for listing disk partitions, using `tree`,
using `watch`, and quickly navigating to parent/ancestor directories.