FCPClientReferenceImplementation: Remove broken, outdated traffic
dumping code

- With fred plugin-fcp-rewrite, traffic dumping is a feature of fred, so
we don't need to reinvent this here. See class FCPPluginClient.
(- The code was broken due to the refactoring to use
fred-plugin-fcp-rewrite: The message handler would not dump messages it
returned to fred. Also, it would only dump the SimpleFieldSet, but the
new fred FCPPluginMessage can contain more data.)
FCPClientReferenceImplementation: Fix outdated JavaDoc

- It was written when the class was an abstract base class which client
applications should extend. Now it is a regular class, and the client
app shall not extend it but implement the interfaces which it provides.
- Also, add proper linebreaks to the JavaDoc and obey the line length
limit.
Merge branch 'master' into use-plugin-fcp-rewrite