feat(packages): switch from yarn to npm

[glebec]

Assignee Tasks

• [x] added unit tests (or none needed)
• [x] written relevant docs (or none needed)
• [x] referenced any relevant issues (or none exist)

Switches package management (removes yarn lockfile, adds npm lockfile, changes Travis options).

[glebec]

Special note, since npm ci tosses node_modules, caching the node modules is counter-productive. Removed from travis yml.