Build embedded Parity JS properly and separatly (#4426)

* Add a specific embed webpack build // output assets in JSON

* WIP Embed

* Updated Webpack

* Update exports // Webpack config

* Fix app build fail

* Fix NPm scripts

* Reduce Embed dependencies

* Fix NPM exports

* remvoe stats

* Lazy-Load worker (not to load in embed)

* PR Grumbles + Fix tests