Remodelled object update cycle. Fixed bugs

Character can now jump! Several problems with the interaction between
collision reaction and the character’s movement were fixed. First it
couldn’t jump, then it would vibrate for this reason the update cycle
was changed to something that should work better for all cases.
Finally the “jumping against wall” bug was fixed, although it might be
cool to re-work that bug into a proper jumping off-wall interaction.
The character might need a more flexible suit!
And finally I can start implementing the level loader and testing ideas!