extract client configuration to separate structure

[stklcode]

The only coonfiguration available up to 1.3 is the API base URL and optionally custom paths to instant and stream endpoint.

Introduce a dedicated configuration structure and corresponding builder to make the configuration more speaking, reusable and easily extensible.

[stklcode]

In 84f0066 a new class has been introduced: UraClientConfiguration and the initialization pattern has been refactored to something like

UraClient client = new UraClient(
    UraClientConfiguration.forBaseurl("...")
                          .withInstantPath("...")
                          .withStreamPath("...")
                          .build()
);