ref #135 Navigation/history

* Adds a history for cgsee navigation. 
* Supports all implemented manipulators and static presets. 
* Adds a gui widget to visualize all saved steps with a small thumbnail.
this is probably unintended code obfuscation - please return ```nullptr``` here. this could further be reduced to return ```m_navigationHistory```, since ```isEmpty checks ```m_navigationHistory``` for nullptr ..