[Java][clients] remove java.lang prefix from Object

Created by: nielspardon

Currently the Java generators generate models with equals and toIndentedString methods that use a fully qualified classname java.lang.Object as the parameter type to compare the object to or generate the indented string for.

I would like to introduce a flag to allow disabling the generation of fully qualified classnames since:

• The PMD source code analyzer flags such an unnecessary use of fully qualified classname by default.
• Other equals method generators like the Eclipse generator generate the equals method with the short classname Object by default.

I'm introducing a new additional property called fullyQualifiedClassnames which is set to true by default to keep the current behavior while allowing to optionally disable the generation of fully qualified classnames for POJOs.

Since I'm not sure whether introducing such a flag is permissible for a minor / patch release I'm targeting this PR at master for now and look forward to your feedback.

@bbdouglas @sreeshas @jfiala @lukoyanov @cbornet @jeff9finger @karismann @Zomzog @lwlee2608 @bkabrda

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