Using lerna with npm breaks various npm commands such as "outodated"
etc.

Switch yarn with namespaces. lerna is only used to run commands on all
packages and maybe publish them etc. yarn 2.x has extra workspace features
like running commands for all packages, so with 2.0 we might also get
rid of lerna.

They are not published yet

It's no longer used.

In the common case of the user just targeting an activity and not
browsing the menu the user wants the menu to be gone right away.

So it doesn't conflict with screenshotting for the docs

Group activity names and descriptions so it's mroe clear what belongs together

No longer depend on env.js to select the right config but require it
to be passed explicitely in the attributes.