Draft: Implement better config management

Use npm package config for configuration management, instead of currently used @beam-australia/react-env.

Pros:

1. It is very popular package under constant development.
2. It is used in Condenser, so people are familiar with it.
3. It allows many config files' formats, like json, yaml, and others, see Configuration Files. These formats do support comments and you get config properties in correct types.
4. No need to run application with strange react-env stuff, like react-env -- next start.

Cons:

1. Environment variables must be mapped to config properties manually, see Custom Environment Variables. However you still get correct types for free this way.

   [Edited] I've just found CLI Custom Environment Variables Generator. This thing should help a little.