Statically register ObjectMapper on class level since it is expensive to instantiate

Statically register ObjectMapper on class level since it is expensive to instantiate

- ObjectMapper objects are expensive to instantiate
- register them statically on the class level instead
  of instantiating them for each invocation
- improve formatting in some of the groovy classes
- change some logger.debug statements to be lazily executed [0]

[0] that is, they are not executed when the log level is higher than debug
    (log.debug(" " + expensiveOperation) vs. log.debug(" {}", expensiveOperation))

Issue-ID: SO-4187
Change-Id: I708c221ff90efb0a27020119253faa549c2ee2fe
Signed-off-by: Fiete Ostkamp <Fiete.Ostkamp@telekom.de>