[Feat] Javadoc documentation for Java SDK

[tomekkolo]

Description Document Java SDK so it is easily usable with any IDE and intelli sense. How documentation should look like ? https://www.oracle.com/technical-resources/articles/java/javadoc-tool.html

Action Items

• [ ] every public function has description including arguments, return values, errors etc.
• [ ] every public interface has description including arguments, return values, errors etc.
• [ ] every public class has description including arguments, return values, errors etc.
• [ ] every non trivial function (or with lot of arguments) has short code sample in description