Updated async-http-client and netty versions to fix Connection leak issue.

Hi Everyone,

My main change is:
<async-http-client-version>1.8.5</async-http-client-version>
<netty-version>3.9.0.Final</netty-version>

I also had to add some plugin versions inside the pom.xml to make it build properly.
I also took the chance and did some tiny refactoring inside the classes.