add 'npm' and 'npm-update' make targets and lockfile (#7246)

* 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

package.json

@@ -1,12 +1,13 @@
 {
   "license": "MIT",
   "devDependencies": {
-    "autoprefixer": "9.5.1",
+    "autoprefixer": "9.6.0",
     "eslint": "5.16.0",
     "less": "3.9.0",
     "less-plugin-clean-css": "1.5.1",
     "lesshint": "6.3.6",
-    "postcss-cli": "6.1.2"
+    "postcss-cli": "6.1.2",
+    "updates": "8.1.0"
   },
   "browserslist": [
     "> 1%",