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.
i prefer if and if-else without brackets if possible, but i'm unsure about best practices.  my point is that the code is bloated by 4 additional lines...
Even more so, sometimes i prefer ```msec < 0 ? m_timer->stop() : m_timer->start(...);```