Change the API for defining client_lib_id

[dlyash]

The approach introduced in #34 assumes that library users will use the following code to set this identifier globally:

LibNameVersionHolder.setClientLibName("name");
LibNameVersionHolder.setClientLibVersion("version");

On my opinion this approach has some severe drawbacks:

• Not straightforward. Users need some sacred knowledge to make use of this API: that there's some class in the library with static methods which affect library behaviour
• Not flexible. No way to specify Client Lib ID on the fine-grained level (i.e. instance of client). Also, static methods mean no way to override them.
• Not testable. Users of the library have to jump through hops to unit-test their code

[dlyash]

@dimitrystd, @PavloMyrotiuk, @dkBrazz let's not forget to discuss this