Create React Apps have the nifty feature of getting environment variables either from the shell or .env files. These are then resolved and baked into the JS bundle by webpack.

When using debug, the entirety of your .env file gets exposed in the bundle, e.g.:

    function u() {
      var e;
      try {
        e = t.storage.debug
      } catch (e) {
      }
      return !e && "undefined" !== typeof r && "env" in r && (e = Object({
        NODE_ENV: "production",
        PUBLIC_URL: "",
        REACT_APP_FOO: "1"
      }).DEBUG), e
    }

This PR fixes that situation by moving the env access to a separate file that isn't accessed when in browser mode.

Also should resolve #467 (comment).