* add 'npm' and 'npm-update' make targets and lockfile
- `make npm` installs and updates node_modules, triggered automatically
on `make css` and `make js` as it completes reasonably fast and
ensures consistent modules.
- `make npm-update` updates all dependencies to their latest version,
regenerates `node_modules` from scratch and updates
`package-lock.json`. It uses npm modules `updates` written by yours
truly to find the latest version of each dependency.
* add suggested make dependencies
* remove package-lock.json during npm-update
* regenerate package-lock.json
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