Rework into npm package

[gganebnyi]

The code should be separated into 2 parts:

• dataprovider: https://github.com/FusionWorks/react-admin-nestjsx-crud-dataprovider/blob/master/admin-ui/src/providers/nestjs_crud/index.js
• example: the rest of the code

Dataprovider should be published as npm package.