Save the full path to dotfiles & add cd functions

The full path to the dotfiles directory will be saved to
`~/.dotfiles_path` when `setup.bash` is run.

Shortcut functions `dotfiles` and `common` were added to automatically
cd to the `dotfiles/` directory or the `dotfiles/shell/common.d`
directory and showing some useful information.
Simplify related aliases

For `ls` and `feh`, don't repeat options set in the base alias.