change eventhandler responsibility. #42

* EventHandler: gets incoming event callbacks and a) handles them (like ESC for end() or F5 for shader reload, or b) pipes them to Navigation and Manipulator (coming soon)
* (EventHandler knows the Game, not vice versa.)
* Navigation: Created by Game, handles navigation...
* Manipulator (coming soon): Created by Game, handles in-world-manipulating events like throwing elements
add Manipulator. #42
remove debug output in EventHandler. #42
add background sound-toggling to Manipulator. #42

* I for rain
* O for piano
make use of GLFWs methods for game ending/window closing. #40

* ESC now calls glfwSetWindowShouldClose(window, GL_TRUE)
* pressing the [X] button at the top right of the window now ends the game and closes the window too
add 'pause command'. #42

* When pressing P, physic updates won't trigger, causing the world to 'freeze'. Navigation etc. still works though.
add updating hand position. #42

calculating world-coordinates of the Hand (not available yet) from the screen coordinates of the cursor.
Merge pull request #44 from lanice/nirvana_eventhandling_40

Nirvana eventhandling 40