Improved the camera.

Camera:
 1. Zooming has been fixed, the camera now zooms at a constant factor of zcps (in settings) per second (optimal: 20).
 2. Movement has been fixed, it is now constant at all zoom factors.
 3. It is possible to both zoom and move at the same time now.

Additional:
 - Removed the zoom update UI element.
 - Introduced the 'keys' dictionary and improved event checking.