Add react-error-overlay package (#2111)

* ༼ つ ◕_◕ ༽つ stack-frame-overlay

* Fix linting

* Remove auto overlay

* Fix e2e

* Pull in the rest

* Appease flow

* Correct dep

* Remove old repo references

* Check flow on test

* Test overlay in e2e

* Add cross env

* Rename package

* Make sure it gets built post-install

* Update the README

* Remove extra builds now that there's a postinstall script

* Revert "Remove extra builds now that there's a postinstall script"

This reverts commit 8bf601d.

* Remove broken script

* Fix some dev ergo

package.json

@@ -5,7 +5,7 @@
     "changelog": "lerna-changelog",
     "create-react-app": "tasks/cra.sh",
     "e2e": "tasks/e2e-simple.sh",
-    "postinstall": "lerna bootstrap",
+    "postinstall": "lerna bootstrap && cd packages/react-error-overlay/ && npm run build:prod",
     "publish": "tasks/release.sh",
     "start": "node packages/react-scripts/scripts/start.js",
     "test": "node packages/react-scripts/scripts/test.js --env=jsdom",