Make slate packages debuggable locally

[kamilmielnik]

Currently there is no easy way to locally test changes in the editor (any package).

The goal is to make it possible to test everything with simple npm start that would run the editor with hot reload of all the packages.

[yuriyyakym]

@kamilmielnik do we have a linear task for this? I cannot find it

[e1himself]

This has been addressed by #48.

Because the release deliverable is now unbundled (with files separated as they were in source code), it's now possible to link this package to the consuming app with npm link and have nicer debugging experience right in your browser with source maps and manageable file names.