Prepare for Lerna NPM package management.

[jrwats]

@public
#90 Any published NPM module will now live under the packages per Lerna best practices. This is not strictly required, but makes our top-level repo slightly more sane, so we might as well abide by the community pattern.

In the process, I'm fixing the paths in yarn scripts in .*demo-apps referencing ../transform here also.

Ultimately we're doing:

transform/* => packages/*
fbt-runtime/* => packages/fbt/*
fb-tiger-hash => packages/fb-tiger-hash

Test Plan:

yarn
cd demo-app
yarn manifest
yarn collect-fbts
yarn translate-fbts
yarn test
yarn start