'chain' is a "slug"-like string that matches the 'chain' field in token
definitions. It is also unique so it can be used as a URL slug in
Connect / webwallet
`cointool.py coins_json` generated an old-style `coins.json` file with
entries on bitcoin-like coins. This is no longe really doing what we
need.
Instead, the new command `dump` will output _all available data_ in the
same format as Python sees it. Much more useful for other kinds of
consumers.
