First shot of refactoring the serialization/deserialization stuff to be independent of any JmxRequest specific stuff.

The goal is better reuse in different places and maye extraction in an own module.
Fixed some unit tests
Changed "maxDepth" to be 1-based instead of 0-based for READ requests.

This change was introduced to harmonize with the other limit values and for how LIST
request use maxDepth (which already is 1 based). Protocol version was bumbep up therefor
to 7.0. Sorry for any inconvenience.
Fixed WriteIntegrationTest
Final unit test fixes related to the JSON serialization stuff.
Added some new unit tests to the core package