Add smoosh_tools subcommand to show known good revisions for m-c + jsparagus

[arai-a]

#569 will add information in ci_smoosh_status branch.
we can get and show them in smoosh_tools

[arai-a]

we could also provide a command that shows (or updates to) the jsparagus revision referred by local mozilla-central,
and optionally shows the result of build/test, if it lives on treeherder.