Add command to change local working directory in `target-shell`

[yunzheng]

Currently there is no way to change the local working directory when you are in target-shell, but can be useful if you want to export something using save to the current working directory or maybe some other commands.

A good way to implement this is to introduce two new commands (sftp also does this for example):

lcd -> local change directory
lpwd -> local print working directory

Or we could also think of adding do_shell which would automatically map ! to this:

!cd <directory> -> shell out and change directory using cd
!pwd -> shell out and run pwd
!ls -la -> shell out and run ls -la.
!<omg code exec> -> shell out and run any arbitrary code..

I think adding do_shell can introduce some security risks (eg: clipboard paste oopsies) so maybe better not. But just adding it here for discussion.