add a cleanup script for normal file system and docker volume

Testing is still manual. In order to do testing with consistent starting conditions, it's necessary to clean up between operations. Documentation or a cleanup script would help so that developers and operators can easily get to a clean state:

• Running with docker ends up with a container and attached volume that require additional knowledge to clean up.
• Running directly or running webpack ends up with several files spread out in the file system that require clean up. Something like git clean -fdxn is useful but risky for people not familiar with it.

Note that verde created a cleanup script although it may have different assumptions on file structure within the repo.