Fragment ground height calculation

Split computeGroundHeight in several functions, to
centralize some code and ease readability
Add EntityPositionChangedEvent and notify the Scene with this Event
Implement multi-platform getTime function
Implement GravityComponent
Add time management in MovementSystem
Implement tests for movement system
Implement gravity effect in MovementSystem
Add a test cube to the application
Merge branch 'application-base' of https://github.com/stevenremot/tlsd-prototype into application-base
Fix pretty cube normals
Merge remote-tracking branch 'refs/remotes/origin/application-base' into application-base
MovementSystem send EntityPositionChangedEvent
Merge branch 'application-base' of https://github.com/stevenremot/tlsd-prototype into application-base
Move test cube
Merge branch 'application-base' of https://github.com/stevenremot/tlsd-prototype into application-base
Fix != operators in vector and add listener
Add gravity to test cube
Replace Entity const references by data copy in RenderEvents
Fix other const references
Add SceneData object which handles the SceneNodes' memory and provides access functions while the Scene handles higher level operations
Begin implementation of CollisionComponent and a simple CollisionEngine (based on Irrlicht)