Use Objects.hashCode, Objects.equals, CloneUtils.clone, CloneUtils.cloneList, remove ObjectUtils

[simon04]

No description provided.

[ChristopherSchultz]

java.util.Objects was added in JDK 1.7 and JFreeChart currently advertises compatibility with JDK 1.6. So until the JDK version is bumped-up to 1.7-or-later, this PR will probably be ignored.

(It's a good idea, though!)

[jfree]

Thanks Simon!