Separate admin & editor from webpack-dev-server

[k1sul1]

Only client.js is used through webpack-dev-server, but webpack-dev-server assumes that admin.js and editor.js are used through it too.

This pollutes the console with errors, and things like build errors also show up in things where they're not wanted.

Fix is to remove admin & editor from entries, and run a separate webpack --watch with config for editor and admin.