[TASK] Port to Java 11 #22

According to Oracle roadmap, Java 8 is in extended support. This is an opportunity to port the library to Java 11. Switch to the next LTS permits improve code with these tasks:

• Finish the modularization of the codebase (JSR 376). #23
• Remove the Rest client in favour to the JVM's HTTP client (JEP 321). #24

Minor improvements are the usage of the local variable type inference (JEP 286) and the local variable syntax fo r lamba parameters (JEP 323)