copy assets rollup module

at package.json we have a module, that should copy files(if needed) while building code to es6 version. and before few last weeks, this module was outdated and not copying our files.
My idea was: move away `data` folder outside of `src` - because at that folder only tests are not static. and have maybe another folder for generated json as well. and when we'll run a build, data from both static and generated jsons will be merged inside of `dist` folder, that actually are publishing at npm