State Logger Rework

[pschillinger]

Introduces a completely new and shiny state logger. Most of it happens behind the scenes, but now:

• it will not only log transitions and operator interactions, but also state-internal events (on_enter, etc.) and userdata (only on level "debug")
• you can fully customize the configuration (see logging.config)
• you can add custom logs, both to the official "flexbe"-namespace loggers and your own loggers
• logged data has yaml format to enable a structured processing

Implementation has not been carefully tested yet, consider it as prototype version.

After merging, I plan to add a new tutorial that explains all customization features.

[pschillinger]

Tutorial has been added to the ROS wiki: Logging Behavior Execution

Will merge this soon.