Provide a version for browser environment

[mshustov]

The browser version of the client can provide limited functionality but with a similar API.
The integration tests must be run in both nodejs and browser envs.

In the first implementation, the client uses webpack to shim http module with a browser-compatible version. This approach doesn't allow us to implement env-specific logic for the network modules, so let's consider implementing a separate http_browser_adapter that might encapsulate browser-specific network logic. The separation can be done on the code level by using a dedicated browser entry point of package.json see https://docs.npmjs.com/cli/v8/configuring-npm/package-json#browser

[slvrtrn]

Closing this as #165 was merged; we also have this now: #162