[all] Rename packages to vercel and add logic to publish legacy package names to npm (#4233)

https://vercel.com/blog/zeit-is-now-vercel

* Updates all org packages from `@now` to `@vercel`
* Updates Now CLI package name from `now` to `vercel`
  * Packages contains `"bin"` entries for _both_ `vercel` and `now` in the package.json
* Updates `now-client` package name to `@vercel/client` (org scoped, for authenticity)

There is also a new `publish-legacy.sh` script which ensures that all the legacy package names (i.e. `now`, `now-client`, `@now/node`, etc.) will still be published as well.

We will remove this legacy publishing logic on Jan 1, 2021.

test/lib/run-build-lambda.js

@@ -1,7 +1,4 @@
-const {
-  glob,
-  getWriteableDirectory,
-} = require('@now/build-utils');
+const { glob, getWriteableDirectory } = require('@vercel/build-utils');
 
 function runAnalyze(wrapper, context) {
   if (wrapper.analyze) {