Fix Segfault caused by std::bad_alloc in RobotUnitModuleLogging

Related to #120

Adds two properties:

• One for the maximum size of the backlog (as it seems to accumulate memory even though it has a maximum retention time)
• One for disabling the backlog altogether, as the memory leak is unrelated to the segfaults on ARMAR-DE

This has been tested on ARMAR-DE for >20min